Uncle Sucker

In every alliance, the United States is the most important member and gives more than it gets in return. American politicians and the American public regularly express frustration with allies’ behavior. In 1959, for example, President Dwight D. Eisenhower lamented that the insufficient defense efforts of U.S. allies in Europe meant that the Europeans were close to “making a sucker out of Uncle Sam.” Things have gotten worse since 1959. Today, America’s alliances act as transfer payments from U.S. taxpayers to taxpayers in allied countries.

History and theory both suggest that hectoring allies is unlikely to produce much change. Allies know that they can pocket the gains from U.S. commitments, then spend their own money in the ways they believe benefit them most. Policymakers should evaluate alliance commitments in the context of the net contributions of U.S. allies to U.S. defense, weighed against the costs and benefits of a non‐​alliance.

The only way to produce more equitable burdensharing is to make allies doubt the strength of the U.S. commitment: the stronger the belief in the U.S. commitment, the harder it is to get allies to defend themselves. Unless policymakers fundamentally change their approach to alliances, there is little hope that defense burdens can be spread more equitably.

In the Washington policy establishment, U.S. alliances are seen as an unqualified benefit to the United States. The consensus view holds that alliances disperse U.S. power more broadly, make it easier to apply, and help defray its costs. Whether they are bilateral or multilateral, alliances are celebrated as net contributors to U.S. national security.¹

But there is a perennial failure to distribute the costs of common defense across U.S. alliances. With few exceptions, the United States spends a greater share of its national income on defense than its allies, despite the fact that it is more secure. An elaborate web of justifications has been spun to argue that alliances confer benefits on the United States that are hard to capture, making this sort of cost‐​benefit analysis either specious or impossible.

Historically, states formed alliances for the purpose of increasing their security.² By pooling their resources and planning for war against a common adversary, states sought to decrease the danger that they would be attacked or increase their chances of winning if they were. When called to account, of course, states have not always honored their alliance commitments. One recent study suggests that in the era before World War II, states honored their commitments 66 percent of the time, whereas in the postwar era, they did so only 22 percent of the time.³

In the years following the country’s Founding, U.S. leaders viewed European great power politics with revulsion and generally abjured alliances.⁴ The exceptions were notable for the extent to which they benefited the United States. The Franco‐​American Treaty of Amity and Commerce was signed in 1778 to establish and solidify the U.S.-France economic relationship, and the subsequent Treaty of Alliance pledged France to the United States’ defense and recognized French holdings in the Americas. This relationship with France helped nurse the American republic to viability, and by 1793, President George Washington declared U.S. neutrality in the war between Britain and France, ending U.S. participation in the alliance with France.

It was only after the end of World War II that the United States began to form treaty alliances around the world. While it is now overshadowed by other alliances, the first major U.S. alliance commitment was under the Rio Treaty of 1947, which brought countries from Tierra del Fuego to the northern U.S. border into alliance with one another. In 1949, the North Atlantic Treaty—also known as the Washington Treaty—created the North Atlantic Treaty Organization (NATO), with its 12 original members committed to the defense of the North Atlantic area. Both during and after the Cold War, NATO expanded, swelling to include 30 nations from the United States to the Russian border.

By contrast with its approach in the Western Hemisphere and Europe, in Asia the United States relied on bilateral treaties, first with the Philippines and Japan (1951); South Korea (1953); and the Republic of China (1954). An early effort at involving outside states in the region produced the Southeast Asia Treaty Organization (SEATO) in 1954, but SEATO dissolved in 1977, leaving behind a U.S. commitment to defend Thailand. Its only other treaty in Asia was the so‐​called ANZUS agreement with Australia and New Zealand, signed in 1951.

In the postwar era, complaining about U.S. allies’ defense spending has been a rite of passage for American presidents. Every president from Dwight D. Eisenhower to Joe Biden has done so. In addition to presidential complaints, Congress has held hearings and performed studies, diplomats and defense officials have pressed their case, but as Figure 1 shows, the U.S. share of allied defense spending has always been much higher than the U.S. share of allied GDP.

Since roughly 1960, the United States has averaged about 36 percent of allied GDP but more than 61 percent of allied defense spending. Why have American policymakers failed to distribute defense burdens more equitably?

Cheap‐​riding by allies (the ride in most cases is subsidized but not free) is probably overdetermined.⁵ First, as the literature has suggested for nearly 60 years, smaller, weaker allies can free‐ or cheap‐​ride on stronger allies because it is rational for them to do so if the stronger allies will pick up the slack. They can safely ignore complaints about burdensharing from their stronger patron.⁶ Second, in alliance relationships, there is a tradeoff between control over alliance policy and the equitable distribution of defense burdens. U.S. policymakers have historically privileged control of America’s allies over fairly sharing the burden of their defense. Finally, U.S. policymakers have acted based on the belief that deterrence is cheap. If deterrence is cheap, alliances with weak, vulnerable members may not be very costly. But an array of new research suggests that the policy of making small military commitments in the form of “tripwires” meant to trigger U.S. involvement in a conflict may be based on a misapprehension about how deterrence works.

This paper proceeds in four parts. First, it recounts the postwar history of U.S. complaints about allied defense spending and U.S. efforts to distribute defense burdens more equally. Second, it presents data showing the distribution of defense burdens in U.S. alliances over time. Third, it draws from the scholarly literature on alliance burdensharing to suggest what policymakers and analysts should expect (and should have expected) to see in terms of successes and failures. It concludes with recommendations for how policymakers can force change in allied defense spending, and the potential tradeoffs involved should they do so.

Presidents have differed wildly over the last 70 years in terms of intellectual style, politics, personality, and myriad other ways. But to a man, they have both undersold the cost of U.S. alliances to the American people while complaining, mostly ineffectually, to U.S. allies about their defense spending.

NATO was not marketed to the American people as a permanent alliance. During a 1949 Senate hearing on U.S. accession to the North Atlantic Treaty, Secretary of State Dean Acheson was asked whether the U.S. role would involve “substantial numbers of troops over there as a more or less permanent contribution to the development of these countries’ capacity to resist?” Acheson responded indignantly that “the answer to that question, Senator, is a clear and absolute NO!”⁷

More than 70 years later, of course, it has become clear that policymakers long have viewed the U.S. commitment to NATO as requiring substantial numbers of troops over there as a more or less permanent contribution to the development of these countries’ capacity to resist.

In the earliest years of NATO’s existence, the Eisenhower administration worked to build up a European “Third Force” that could replace U.S. exertions in Europe. Secretary of State John Foster Dulles threatened an “agonizing reappraisal” of the U.S. commitment if the Europeans could not draw up a treaty between Germany, France, and the Benelux countries that would lay the foundation for an autonomous European defense.⁸

The Eisenhower administration failed. By 1959, 10 years after NATO’s founding, Eisenhower complained bitterly to his leading military officer in Europe about European countries’ willingness to let Americans carry much of the burden of their defense. Lamenting that “other than himself, he thought no one else is taking the problem seriously enough,” a memo described Eisenhower’s view that

Eisenhower handed the presidency—and responsibility for complaining about European cheap-riding—to John F. Kennedy. By 1963, Kennedy declared that

After Kennedy’s assassination, the growing crisis in Vietnam consumed much of his successor’s attention, but President Lyndon Baines Johnson struggled with a new and burgeoning balance of payments crisis brought about in part by the presence of large U.S. forces overseas, particularly in Europe. Johnson negotiated an agreement with his counterpart in West Germany, albeit one that did not make the costs of German defense German or rectify the balance of payments problem.¹¹

Similar to Johnson’s, President Richard Nixon’s foreign policy focused disproportionately on Southeast Asia. Still, during a 1969 press availability in Guam that would lay the foundation for the Nixon Doctrine, which itself was focused on redistributing defense burdens from the United States onto allies and partners, the president announced,

Nixon’s diagnosis of the problem was consistent with what presidents before him and those who would follow knew: “if the United States just continues down the road of responding to requests for assistance, of assuming the primary responsibility for defending these countries … they are never going to take care of themselves.”¹³

By the end of the Nixon administration and into the administration of Gerald Ford, Congress had grown exasperated with European efforts. Starting in the 1960s, Senator Mike Mansfield (D‑MT) had pushed the so‐​called Mansfield Amendment, attached over the years to a variety of bills, which called for a large reduction in the U.S. forces in Europe.

The United States experienced severe economic volatility in the 1960s and 1970s. Inflation damaged the economy, and the dollar’s valuation changed wildly after Nixon closed the gold window. In particular, as historian Francis Gavin wrote, U.S. policy in Europe had showed “a repeated pattern of sacrificing economic for geopolitical interests.”¹⁴ Those economic sacrifices began to impact U.S. politics, which yielded the Mansfield Amendment of 1971.

Lamenting that the United States was “carrying a very one‐​sided burden” in NATO, Mansfield’s amendment would have cut the U.S. presence in Europe by roughly half by the end of 1971. The Nixon administration lobbied furiously against the measure and prevailed throughout 1971.¹⁵ In 1973, however, a similar amendment passed until it was overturned the same day on an arcane parliamentary procedure, again in response to forceful lobbying by the administration.¹⁶

In response to the Mansfield Amendment, the Europeans “invented,” to use Henry Kissinger’s word, a new set of negotiations with the Soviets that were designed to help the administration “stop Mansfield.”¹⁷ The idea was that the United States should not make any unilateral changes to its forces while negotiations on forces in Europe were ongoing. Those negotiations went nowhere, but they did help to stop Mansfield. However, they did not solve the larger problem of congressional discontent with European burdensharing.

In 1974, the Jackson‐​Nunn Amendment replaced Mansfield’s efforts, overwhelmingly passing in the Senate. In a sense, Jackson‐​Nunn foreshadowed President Donald Trump’s conception of alliances as protection rackets.¹⁸ Jackson‐​Nunn did not question whether enormous U.S. deployments were required for U.S. security; instead, it called on the Europeans to offset a larger share of the costs of basing U.S. forces in Europe, or else face U.S. troop cuts to make up the difference. The bill was effective, extracting German purchases of U.S. goods and offsetting close to $2 billion of balance of payments expenditures.¹⁹

Jimmy Carter ran for office in 1976 pledging to withdraw U.S. troops from Korea, based on the judgments that they were not necessary to defend South Korea and that support for the autocratic regime in Seoul was in conflict with U.S. values. As president, he attempted to follow through on this commitment, but the military, intelligence community, Congress, members of Carter’s own bureaucracy, and the governments in Seoul and Tokyo coordinated their efforts, successfully squashing Carter’s initiative.²⁰

In the 1980s, burdensharing concerns again drew the attention of politicians. In particular, Japan’s economic rise led Congress to propose dramatic measures to offload the cost of defending Japan. The powerful North Carolina senator Jesse Helms (D‑NC) proposed renegotiating the U.S.-Japan treaty to make it reciprocal. Again using the logic of alliances as protection rackets, a North Carolina congressman proposed a 2 percent “security tax” to be paid to the United States by the Japanese in exchange for defending them.²¹

In 1982 the Defense Department, under Secretary Caspar Weinberger, began to publish a series of papers called “Report on Allied Contributions to the Common Defense.” These reports regularly admitted that no matter how burdensharing is measured, the United States was carrying a disproportionately high share of the defense burden inside its alliances. At the same time, in these reports the Defense Department always acted as a defense lawyer for U.S. allies. Richard Perle, who had been in charge of the report early in the Reagan administration, admitted that the methodology involved “thinking of ways to put the best possible gloss on some pretty dismal figures … we look for statistics that make the allies look good.”²²

By the late 1980s, the House Armed Services Committee had grown exasperated with the Reagan administration’s failure to produce more equitable burdensharing and convened a number of hearings with scholars and outside experts to examine the question. The committee produced a report in August 1988 sharing the findings of its research. It concluded sourly:

• “Despite the assertions of U.S. Government officials that the allies are constantly urged to assume more defense burdens, the statistics suggest that U.S. diplomacy has largely failed to bring about more equitable burdensharing.”
• “On the whole, it appears that the United States has not adequately emphasized burdensharing with the allies.”
• “As long as the United States shows a willingness to assume disproportionate burdens, the allies will permit us to do so … when the allies become aware that we are not going to step forward and assume a disproportionate responsibility, then and only then will they step forward to assume their share of the responsibility.”²³

As the committee’s chair, Representative Pat Schroeder (D‑CO), warned,

Issued just a year before the beginning of the end for the Soviet Union, however, the report’s terse conclusions were overtaken by events.

Even so, the 1988 presidential campaign featured unanimity among the candidates that “European members of the North Atlantic Treaty Organization have been freeloading at American expense,” the Washington Post reported. “In these times of deficits and the falling dollar, [that line] has been a sure applause‐​getter from audiences of the left, right and center.” The eventual winner, George H. W. Bush, declared that “we must ensure that they carry their fair share of the load.”²⁵

The administrations of Bill Clinton and George W. Bush both moved from complaining about burdensharing to trying to smother European efforts to do more autonomously on defense. For example, when the Europeans began to work haltingly on non‐​NATO security cooperation in the 1990s, the U.S. policy establishment went into overdrive. Secretary of State Madeleine Albright announced that European efforts must not “in any way undercut NATO,” and that these would be viewed unfavorably if they diminished, discriminated against, or duplicated NATO capabilities.²⁶

In 2003, as Europeans again began work on non‐​NATO defense cooperation, U.S. Ambassador to NATO Nicholas Burns denounced such plans as “one of the greatest dangers to the transatlantic relationship.”²⁷ It is striking that Burns did not warn of a danger to NATO as an institution, or of a danger to U.S. leadership in Europe, but of a danger to the transatlantic relationship itself. If the United States could not dominate European security, it would view Europe as something other than a partner.

Complaints about European contributions continued through subsequent administrations. Robert Gates, defense secretary to presidents Bush the Younger and Barack Obama, left office under a cloud of frustration over NATO. At the U.S. National Defense University in February 2010, Gates lamented that “The demilitarization of Europe … has gone from a blessing in the 20th century to an impediment to achieving real security and lasting peace in the 21st.”²⁸ In another speech in June 2011 in Brussels, Gates lamented that European defense budgets “have been chronically starved for adequate funding for a long time, with the shortfalls compounding on themselves each year,” and warned of “the very real possibility of collective military irrelevance.” Pushing the point further, Gates warned of the prospect of a “dwindling appetite and patience” among Americans to spend resources on behalf of European states “apparently willing and eager for American taxpayers to assume the growing security burden left by reductions in European defense budgets.”²⁹

For his part, Gates’s last boss, Obama, admitted to The Atlantic’s Jeffrey Goldberg in 2016 that “free riders aggravate me,” and that he had leveled an ultimatum at British Prime Minister David Cameron: Great Britain would no longer be able to claim a “special relationship” with the United States if it did not commit to spending at least 2 percent of its GDP on defense.³⁰

Six years after Gates’s last NATO speech, Trump was U.S. president and Gates’s warnings looked both eerily prescient and understated. Trump’s long‐​standing skepticism about the value of U.S. alliances came to a head leading up to the 2018 NATO summit, when he repeatedly mentioned his desire to remove the United States from NATO, only to be outmaneuvered by his advisers working in conjunction with NATO bureaucrats.³¹ Trump also cast doubt on the U.S. alliances with Japan and South Korea, announcing before a trip to Japan that “almost all countries take tremendous advantage of the United States,” and that “if Japan is attacked, we will fight World War III.… But if we’re attacked, Japan doesn’t have to help us at all.”³²

President Biden has been far more conciliatory toward NATO, repeatedly referring to the long‐​standing alliance as a “sacred” U.S. commitment.³³ In keeping with the emphasis that U.S. policymakers have placed on reassuring allies who express fear, after the Russian invasion of Ukraine in February 2022 Biden sent an additional 20,000 troops to Europe to soothe European anxieties about Russia.

This paper, like all others that attempt to measure “defense,” let alone its burden across countries, must concede that any effort to quantify defense exertion is crude and imprecise. Most studies have examined defense spending as a proxy for defense, but there is more and less effective defense spending. Defense spending is not fungible across domains, or all theaters. Moreover, war‐​fighters and materiel only make up a portion of military effectiveness. National will, military organization, and an array of other factors weigh heavily on national defense.

Further, comparing U.S. defense spending against the spending of its allies brings with it additional hazards. Because the United States has so many alliance commitments around the world, comparing, for example, how many allies spend a given share of GDP on defense can miss the point. The United States has wealthier, more important allies, and poorer, less important ones. If the wealthier ones are doing their share, what the smaller ones do is less important. Similarly, no matter how hard the smaller ones work, they cannot shift burdens meaningfully.

Unfortunately, some of the highest spending allies as a percent of GDP are so small as to be militarily irrelevant to almost all major conflict scenarios, and some of the wealthiest and most important allies are some of the worst offenders on low defense spending. Figure 2 evaluates U.S. spending as a share of GDP against non‑U.S. allied defense spending as a share of non‑U.S. allied GDP, collectively.

Since the larger, wealthier states tend to spend relatively less of their income on defense, counting the number of allies spending a given percent of national income on defense gives an unduly rosy view of the distribution of defense burdens. Still, it is worth examining cases in which defense burdens did tip in the U.S. favor.

Because policymakers have so consistently assured allies of the strength of the U.S. commitment to their defense, it is difficult to find evidence that declining to reassure, or even cultivating fear of abandonment, works. However, because there are so few cases, we can select on the dependent variable to limn the historical record for the best explanations about why certain countries chose to increase their efforts. Taiwan and Japan represent notable cases.

The 1970s saw massive changes in U.S. policy toward the Republic of China (ROC, now known as Taiwan). From the Nixon administration beginning its opening to the People’s Republic of China (PRC) in 1970 to the Carter administration ultimately swapping diplomatic relations from the ROC to the PRC in 1979, the ROC government on Taiwan got the short end of the deal. The PRC government made marginalization of its vanquished foe a priority throughout negotiations with the United States.

In the years leading up to the swap of formal relations, the ROC government could see the writing on the wall. As Figure 3 shows, even as its economy was growing rapidly, the share of GDP that Taiwan dedicated to defense more than doubled from 1977 to 1979.³⁴

With Taiwan spending closer to 2 percent of GDP on defense today—while facing a much worse security environment—it is worth asking why the disparity between Taiwan’s willingness to exert itself on behalf of its own defense in the 1970s and 1980s ebbed between that era and today. Dismally, one of the most thorough examinations of this question concludes that “the transition to democracy … increased the incentives for Taiwanese political leaders to free‐​ride on the American alliance, while making it more difficult for the American side to influence policy decisions in Taiwan.”³⁵

Japan is another notable case of burdenshifting. Scholars have made much of Japan’s postwar anti‐​militarism, and they have tended to attribute its low levels of defense exertion to ideology. However, starting in the late 1970s, the Japanese security environment began deteriorating, and the United States did not rush in to the breach to remedy it. As Dartmouth’s Jennifer Lind observes, the Soviet Union was expanding its Pacific Fleet at the same time that the United States was removing military assets from the Asia‐​Pacific region. The United States had withdrawn from Vietnam and, under President Carter, was looking to withdraw from Korea. By 1982, the Soviet Pacific Fleet out‐​displaced the U.S. Seventh Fleet by a factor of almost three‐​to‐​one.³⁶

As seen in Figure 4, Japan responded to this significant worsening of its security environment by increasing defense spending. During the period from 1980–1993, Japan’s defense spending as a percentage of GDP increased by more than 200 percent. Given that during this same period Japan’s economy was roaring (making the denominator of defense as a share of GDP increase), this boost in defense expenditures constituted a meaningful improvement in Japanese military power. When the world looked scarier and the United States declined to assure Japan that Washington would handle the problem itself, Japan balanced against danger. Arguably, a similar process is taking place in Tokyo today.³⁷

These two cases should not be taken as proof that Washington can burdenshift by doing less for its allies, but they certainly suggest it. The logic of burdenshifting appears to have worked in these two cases where allied defense spending rose significantly in the face of rising danger that the United States did not appear to meet on its own.

U.S. officials have attempted to persuade their treaty allies to increase their defense exertions through exhortation. However, this approach has failed to distribute the defense burden more evenly. This section examines the scholarly literature on alliances and draws conclusions about how and why U.S. efforts have failed.

As seen in the previous section, American elites’ failure to distribute defense burdens more equitably is not due to inattention to the problem. Rather, one of the oldest findings in the literature on alliances is that an alliance partner as disproportionately large as the United States is destined to carry an outsized share of the defense burden, provided the allies believe in the larger state’s commitment to their security. The incentives of alliance members, coupled with a belief in the strength of the U.S. commitment to them, make it impossible to produce equitable burdensharing.

The seminal study evaluating burdensharing in alliances is an article from 1966 by Mancur Olson, Jr., and Richard Zeckhauser. In it, Olson and Zeckhauser conceive of security within an alliance as a public good, and show that, if the allies value that public good, smaller states can rationally shirk because larger states will rationally overpay to produce security.³⁸

Since that article was published, scholars have used Olson and Zeckhauser’s framework to test whether smaller allies free‐ or cheap‐​ride on their larger patrons. However, as with most large literatures, scholars have quarreled with several aspects of the initial model and its application to burdensharing.

First, scholars have disputed Olson and Zeckhauser’s specification of defense as a pure public good. Since one unit of defense exertion does not confer equal benefits on all members of an alliance, only some portions of defense should be conceived of as pure public goods.³⁹ In addition, any individual alliance member’s policy goals may not overlap perfectly with those of other members, and thus its defense acquisitions and policies may not contribute to the provision of a pure public good within the confines of the alliance.

An additional complicating factor is that all available measures of defense effort are imperfect: defense budgets, for example, are used as a proxy for fighting capability but they measure capability only crudely. Budgets cannot account for factors that are important to the provision of defense, such as national will or morale.⁴⁰ Further, because the size of a nation’s economy is used as part of both the independent and dependent variables (GDP and defense spending as a portion of GDP), scholars have pointed out that changes in economic growth affect both variables simultaneously, limiting the ability to isolate one variable’s effect on the other.⁴¹

Despite the voluminous debate about methods and the variety of conclusions, an array of recent findings on alliance burdensharing are notable: one recent study found little evidence of cheap‐​riding from 1967 through 2009, but showed that after 2009 there was “indisputable evidence … of an exploitation of the large, rich allies by the small poor allies,” which it attributed to NATO’s expansion to include an array of small, weak, vulnerable members.⁴² Another discovered that deploying U.S. troops in a country tended to produce a decrease in the size of that country’s armed forces and to make it more likely to initiate a militarized international dispute; it also failed to produce additional deterrence of the country’s adversaries.⁴³ A third study found that rather than being merely a consequence of the size of the allies, allied contributions to common defense turn on “great‐​power patrons’ ability to exploit their allies’ fears of being abandoned.”⁴⁴

Beyond the difficulty of producing equitable burdensharing among allies of different sizes is the tradeoff between the desire to control allies’ policy versus the desire to have them carry a larger share of the burden of their own defense. The more control over its allies a large country seeks, the less likely those allies are to carry an equitable share of the burden for their defense. For example, the hub‐​and‐​spokes system of bilateral alliances in Asia was designed with the explicit aim of dominating U.S. allies’ security policies. By making the United States the “hub” of the system and keeping allies as individual “spokes,” Washington policymakers made it difficult for Asian allies to pursue independent policies.⁴⁵

To a lesser extent, the tradeoff between control and burdensharing affects NATO as well. For example, Christopher Layne of Texas A&M traces U.S. thinking before, during, and after the Cold War to argue that, at a minimum, U.S. policy in Europe sought not just to defend against the Soviet Union, but also to strangle European security cooperation in the cradle and to dominate European security itself.⁴⁶ U.S. policymakers have, until recently, firmly opposed the creation of European security institutions that could take some of the burden off of NATO/​the United States. The reason is that the United States prefers outsized influence on its allies’ policy, which it gets from being the cornerstone of security in their various regions.

This monomania for control makes equitable burdensharing much more difficult. It is also unnecessary for U.S. national security. The militarily important parts of Europe, for example, would not kowtow to Russia in the absence of U.S. leadership. It is unlikely Russia could even plausibly demand that they do so. Similarly, a more coherent and cohesive European Union effort to defend Europe from Russian predation would not threaten U.S. interests on the continent. If anything, the Russian blundering in Ukraine has demonstrated the limits of conventional Russian military power.⁴⁷

Many U.S. alliance commitments have relied, and currently rely, on tripwire logic. That is, Washington does not aim at troop deployments that decisively shift the conventional balance in a given theater; rather, policymakers count on the idea that even small deployments of U.S. forces implicate U.S. credibility because, should war break out, the deaths of U.S. servicemembers would necessarily produce a larger U.S. response. As Thomas Schelling put it, the function of tripwire forces is to

The internal logic, if perhaps not the ethics, of this approach to deterring attacks on allies works fine. Tripwire forces are used to signal that, should conflict erupt, Americans will be killed, Americans’ national fury will be aroused, and a larger U.S. response is sure to be forthcoming. One can see how the idea of buying deterrence for cheap—that is, without paying for the forces that would be required to tip the military balance in every theater—appeals to policymakers. Given the number and scale of U.S. alliance commitments, it would be enormously costly to try to dominate every region where U.S. allies feel threatened.

However, a growing body of research based on both historical analysis and survey experiments suggests that tripwires do not effectively deter adversaries or reassure allies. Several recent studies suggest that the causal pathway from limited deployments to deterrence via tripwire logic does not hold up. Instead, these studies conclude, military forces that tip the local balance of power in favor of defense are required for stable deterrence.⁴⁹

One response to this scholarship would be to ask why, if they don’t deter, aggressors haven’t tested U.S. tripwires? There are two possible answers. First, Dan Reiter and Paul Poast argue that the withdrawal of most, but not all, U.S. forces from Korea between 1949 and 1950 arguably convinced North Korea that it could win quickly, thus leading to the Korean War.⁵⁰ In that case, a tripwire did not deter. Secondly, war has been overpredicted and in many cases peace may be overdetermined. As one example, U.S. policymakers, like Schelling, assumed that the presence of tripwire forces in Berlin prevented a Soviet invasion of West Germany. Subsequent historical work makes clear that the tripwires were not deterring: the Soviets had no intention of invading West Germany.⁵¹

Policymakers should seriously consider this body of research. Having emphasized a tripwire strategy in theaters from the Baltic states to the Korean Peninsula, a lot is at stake should this approach not produce its intended effect. It is worth noting that the prime minister of Estonia, a country whose security relies largely on tripwire logic, stated in June 2022 that the war in Ukraine proves that “this tripwire concept doesn’t really work,” despite the fact that Ukraine did not have a tripwire.⁵² One NATO diplomat remarked similarly in May 2022 that “we think it’s time to move on from this forward presence concept based on the tripwire approach” in places like the Baltic states, toward a forward deployment big enough to tip the conventional balance. In the terms of defense strategy, as that diplomat put it, the new vision would move from “deterrence by punishment to deterrence by denial.”⁵³

NATO admitted Estonia, Latvia, and Lithuania as members in 2004, but did not have plans for their defense until 2010, after having been lobbied by the Baltic states to develop them after the Russo‐​Georgian War of 2008. In response to that lobbying, the alliance did include the Baltic states in NATO plans, with a cable from U.S. Ambassador to NATO Ivo Daalder urging NATO countries to assure Russia by stating that its defense plans were “an internal process designed to make the Alliance as prepared as possible for future contingencies” and “not ‘aimed’ at any other country.”⁵⁴

In less than 20 years, then, NATO has moved from no defense plan for the Baltics, to a tripwire defense plan, to a discussion of maintaining enough NATO troops on their territory to overwhelm any Russian advance. The requirements of defending the Baltics were ignored during these countries’ accession, then undersold and possibly misunderstood altogether. Since the number and scale of U.S. alliances makes it impossible to move to a deterrence‐​by‐​denial approach in all theaters, if tripwires do not work as advertised, some U.S. alliance commitments may have to be revised to defend others.

The scholarly literature discussed above suggests that alliance burdensharing is a tough problem to solve and that the failure to solve it is in part a function of collective action dynamics, the U.S. desire to control its allies’ foreign policies, and a belief that deterrence, via tripwire logic, is cheap.

The responses of scholars who support the U.S. alliance system have varied. One point on which many seem to agree is that alliances cost the United States nothing. Mira Rapp‐​Hooper, a Council of Foreign Relations scholar now serving in the Biden administration, writes that “alliance agreements themselves impose no financial burdens on the U.S. Treasury. What costs money—and potentially lives—is the associated force posture.”⁵⁵ Alexander Cooley and Daniel Nexon agree: “How much the United States spends, either directly or indirectly, on its formal alliances is almost entirely a matter of policy decisions and political processes,” not the alliances themselves.⁵⁶

This argument does two things: it shows how deeply ingrained is the dedication to U.S. alliances in the foreign policy establishment and it hides the ball on substance. The strategy of forward defense via commitments to far‐​flung allies logically implies defense efforts in support of the alliances. Alliances without military forces to support them would have “no more force than a flapping sheet of paper,” in historian Geoffrey Blainey’s phrase.⁵⁷ Debates over burdensharing instead ask who should pay what share of the costs for defense, and whether the current arrangement can produce that result. Because its allies have shirked effectively for decades, the United States has paid, and continues to pay, more than its share of the tab.

As Jeremy Shapiro writes,

Studies that isolate alliances from other factors show that they are associated with increases in defense spending. In one statistical model used to estimate the financial cost of U.S. alliances, Joshua Alley and Matthew Fuhrmann judge that one alliance adds between $11 and $21 billion to U.S. defense spending. Looking in particular at the cost of admitting the Baltic states to the alliance in 2004, Alley and Fuhrmann estimate that by 2019, admitting the Baltic states added between $16 and $45 billion to the U.S. defense budget.⁵⁹

Another study, using very conservative assumptions, estimates that shedding the conventional military commitment to Europe, while retaining extended nuclear deterrence and high‐​level naval and intelligence support to the continent, would save the United States on the order of $70–80 billion per year.⁶⁰ Serious studies have judged that there would be sizable costs to the United States of further NATO expansion and that the U.S. presence in Japan and South Korea carries significant costs.⁶¹ One thing is clear: alliances are not free.

Some alliance advocates argue that the United States should not want fairer burdensharing. Rapp‐​Hooper argues that since alliances aim at controlling allies’ policies, it is wrong to complain about allied cheap‐​riding. Moreover, she writes, the United States and its allies “had different national security objectives”: the allies merely “sought to defend themselves and contribute to the alliance within their regions,” whereas the United States was “spending on a global force posture to prevent Europe and Asia falling under Soviet control, a condition that strategists believed would pose an existential threat to the homeland.”⁶²

The United States spending on a global force posture to prevent Europe and Asia from being dominated by another country is what allowed its allies’ definitions of “defending themselves and contributing to the alliance within their regions” to be so unimpressive. Today, since Russia cannot possibly threaten to bring Europe under its control, and because there are significant geographic and technological grounds for doubting that China could do so in Asia, outright U.S. domination of these regions is unnecessary.⁶³

These counterarguments obscure realities that don’t require elaborate theories or analysis. The defense of Poland matters more to Poles than it does to the United States. But the United States, with a far superior geographic and power position than Poland, spends more of its national wealth on defense than does Poland. If we assume that the overall amount of defense being produced for Poland is optimal, then the U.S. alliance with Poland serves as a net transfer from U.S. taxpayers to Polish taxpayers. One can replicate this syllogism with Japan, Germany, or any number of other U.S. allies.

One frequent denunciation of Trump’s foreign policy is that it was “transactional,” whereas U.S. foreign policy is supposed to operate based on high principle.⁶⁴ But as U.S. allies have frequently made clear, their own interests in the alliances are nakedly transactional. Take, for example, the message of Polish President Andrzej Duda to Polish troops in Afghanistan during a 2018 visit. Duda explained that the reason Polish troops were in that country was not about Afghanistan at all:

That this arrangement benefits Poland seems clear. How it benefits the United States is less so, particularly considering the terrible strategic judgment in Washington that underpinned the mission in Afghanistan. But Europeans’ view of their contribution to NATO as being “a fee to obtain U.S. protection” appears to remain intact.⁶⁶

U.S. allies view their security in transparently transactional, self‐​interested terms. Despite the extraordinary costs borne by U.S. citizens on their behalf, American security commitments have failed to slake the thirst of U.S. allies. Just as prospective allies and partners plead for new American commitments, existing allies and partners demand more American attention. They are need factories. As one former Pentagon official remarked in 2019, America’s partners in the Middle East “are always trying to get us to pour more concrete.”⁶⁷ More recently, Derek Chollet, counselor to the Biden State Department and a longtime Washington foreign policy hand, remarked that in Europe, the Middle East, and the Indo‐​Pacific “and I experience this every day here … there’s a desire for more of the United States, more of our time, more of our energy, more of our attention, more of our force posture.”⁶⁸

To understate, when alliance decisions are considered in American politics, costs in the billions per year are not discussed with U.S. taxpayers. As one study observed, “in the context of NATO enlargement, budget‐​maximizing bureaucracies have every incentive to exaggerate the benefits of enlargement and underestimate its costs.”⁶⁹ Moreover, since the costs come later and tales of U.S. leadership and the rules‐​based liberal international order are told immediately, voters perceive benefits without costs. One analogy would be a firm’s off‐​balance sheet liabilities: they exist but are not reported or accounted for in real time, and can be ruinous when they come due.⁷⁰

Finally, U.S. domination of its allies’ security and its failure to demand that allies do more for their own defense has encouraged allies to adopt priorities that outstrip their own power. Countries that are not even the main security providers in their own regions have taken on grandiose aims on the other side of the globe. Increasingly, French and German leaders, for example, have declared themselves Pacific powers, ostensibly out of concerns for commerce or tiny overseas territories. Given the trivial military contributions they make in the Asia‐​Pacific region, and their shirking when it comes to defense of their own territory, Washington should refuse to coordinate policy with such allies outside their regions until the United States has fully handed these nations’ own security back to their leaders and voters.⁷¹

Policymakers should do several things to force allies and partners to take on a larger share of the burden of their defense. These fall into three categories: institutions, military deployments, and diplomatic signals. First, the institutions that govern U.S. alliances are old, but U.S. relative power means they must respond to demands—not meek suggestions—from Washington. Washington should begin making demands. Second, where the United States deploys and bases troops has a significant impact on allies’ perceptions about U.S. willingness to fight on their behalf and, by extension, what they need to do for their own defense. Policymakers should publicly reevaluate U.S. overseas deployments. Finally, the United States can muddy the signals it sends about where and under what circumstances it is willing to fight for its allies’ interests.

Getting Europe, in particular, off the security dole should be an important task for U.S. policymakers. With little prospect that the United States can dominate the security environments in Europe, the Middle East, and Asia simultaneously without massive increases in the defense budget, and with little sign that massive increases in the defense budget are forthcoming, savings become more attractive. If spending taxpayer dollars on Europe’s defense is not merely unfair but also unnecessary, it becomes doubly lamentable.

In the wake of Russia’s dismal performance bullying its smaller, weaker neighbor Ukraine, and the large dent that Ukraine has put in Russian armor and infantry, it has become clear that Russia cannot defeat Europe’s larger, more powerful countries. If the aim of U.S. policy in Europe is merely ensuring that no one country can dominate Eurasia—achieving “regional hegemony” in international relations jargon—that objective requires exactly zero U.S. exertion.⁷²

One can see both the phenomenon of unequal burdensharing and its consequences in the disparate costs borne by the United States and European countries in arming and attempting to shore up Ukraine’s position as it defends itself. According to the Kiel Institute for the World Economy’s Ukraine Support Tracker, as of this writing, the United States has provided 72 percent of military aid to Ukraine and 59 percent of overall aid to the country.⁷³ Europeans found themselves “almost bystanders in a crisis that might result in a large‐​scale Russian invasion of Ukraine or a new divide in Europe.”⁷⁴ A North American country has taken the initiative for dealing with a European problem, despite the fact that NATO Europe has more at stake than the United States and has a GDP roughly equivalent to it. In Ukraine, the Europeans, savvily, have passed the buck yet again. The Americans, out of profligacy and inertia, have caught it.

U.S. policymakers should publicly announce that they have no intention of supporting any further expansion of the NATO alliance. This would send shockwaves through Europe, making it clear that U.S. attention to Europe is likely to wane. It would also make it clear that the United States does not have any intention of making security guarantees to Ukraine or Georgia similar to NATO’s Article 5—the collective defense provision of the North Atlantic Treaty. This would also likely make the weaker, more vulnerable NATO member‐​states seek more cooperation from major European countries as well as asymmetric capabilities of their own.

To drive this point home, U.S. policymakers should also make it clear that the next Supreme Allied Commander for Europe (SACEUR) will not be an American, and that the Europeans must decide on a European commander. Since the alliance’s inception, the SACEUR has been an American, with his deputy being a European. This gets things backward. Europe should be in the driver’s seat for European security. Once the Europeans settle on a candidate, the U.S. president should make it clear that he will nominate that person and offer to make his or her deputy an American.

A second way to press the issue is by resuming the withdrawal of U.S. troops from Germany that was initiated under Trump and rescinded by Biden before the war in Ukraine. Trump had moved to withdraw roughly 12,000 servicemembers from Germany, redeploying some elsewhere in Europe and bringing some home. Biden paused, then rescinded that move on taking office.

Despite these deployments, after the start of the Ukraine war, Europeans were shaken from their slumber. German Chancellor Olaf Scholz announced a Zeitenwende, translated as a “watershed,” or the change of an era. Scholz announced a €100 billion fund to spend on German defense over the next four years, and that Germany would thereafter meet the 2 percent of GDP spending target on military spending. The measures had support from large majorities of the German public in all the polling done on the announcement.

However, in the intervening months, things changed. The Biden administration sent 20,000 more troops to Eastern Europe and announced new initiatives that it would be taking on behalf of European security. It supported the expansion of NATO to Finland and Sweden. In other words, it recentered European security on the United States.

Shortly thereafter, Germany announced that it would be cutting defense spending. The €100 billion fund would serve mainly as an accounting gimmick to obscure this fact. By 2026, at the end of the four‐​year period covered by the €100 billion, Germany would be spending less on defense than it did in 2022.⁷⁵ This phenomenon, where a crisis erupts, European states get good press for doing more, then both the crisis and the doing more fade away, characterizes how efforts to distribute defense burdens have worked historically. It is time for the United States to wise up.

Resuming the withdrawal of troops from Germany would deliver a shock to Europe in general but to Germany in particular, hopefully reinvigorating the renewed sense of purpose that surrounded the launch of the Zeitenwende in the first place.

The third way that the United States could force greater burdensharing in Europe as well as Asia would be to stop reassuring allies that their most expansive definitions of their interests are covered under their treaties with the United States. With respect to Japan, for example, Obama was quick to assert that the Senkaku Islands, a small group of uninhabited islands disputed with China, were covered by the mutual defense treaty with the United States.⁷⁶ While Obama’s supporters would argue that this move reassured the Japanese about the strength of the U.S. commitment to their security, the way to elicit Japanese exertion is to arouse Japanese anxiety. A country that is completely reassured is also completely lacking in drive to increase its own defense efforts.

Congress should help force the issue. From the 1980s until the early 2000s, the Defense Department was required every four years to submit to Congress a report entitled “Allied Contributions to the Common Defense.” Although this normally involved DOD acting as lawyer for U.S. allies and explaining that if you change methodologies, you can see our allies are actually doing quite a lot, it provided fodder for discussion in Congress about burdensharing both in NATO and in U.S. alliances in Asia. There has been an effort to reinstate the report in the 2023 National Defense Authorization Act; as of this writing, it is unclear whether that will remain in the bill.

There is also precedent for Congress to examine burdensharing in NATO and other U.S. alliances. The 1988 House Armed Services Committee Defense Burdensharing Panel issued a report stating “in the strongest possible terms that Europeans had better be prepared to defend their own territory without a large‐​scale U.S. ground commitment, because that commitment cannot be guaranteed forever.” It suggested further that “the major reason the United States is shouldering a disproportionate share of the defense burden is that … [a]s long as Americans pay most of the cost and assume most of the risks and responsibilities for the defense of the free world, the allies will be prepared to let the United States do so.”⁷⁷ Congress should play hardball with U.S. allies, on behalf of the U.S. taxpayers, who pay for the expansive visions of the U.S. foreign policy elite.

U.S. policy on defense burdensharing has been stuck for decades and remains stuck. History and theory both suggest that no amount of caterwauling from policymakers is likely to spread the burden of defending allies more equitably. Even the Russian invasion of Ukraine and China’s growing threat to Taiwan have failed to encourage the most important U.S. partners and allies to step up. This paper has argued that historical evidence and international relations theory point to the same answer: Washington’s efforts to reassure U.S. allies have worked too well. U.S. allies and partners are confident in the trustworthiness of U.S. commitments and the power with which they are backed.

There is a zero‐​sum tradeoff between reassurance and burdensharing.⁷⁸ Washington reassures its allies and partners, both in order to strengthen deterrence against external threats and to maintain as much control as possible over those partners and allies. As political scientists John Schuessler and Joshua Shifrinson write, however, “it is worth underscoring that there is such a thing as too much reassurance.”⁷⁹ U.S. allies today are too comfortable in the U.S. embrace.

Policymakers should allow U.S. allies to worry about the strength of the U.S. commitment if they want more exertion from these allies. To the extent U.S. allies and partners are reassured of the strength and adequacy of the U.S. commitment to their defense, shirking becomes rational. Until now, policymakers have prioritized U.S. reassurance, which has led to having allies that spend less of their own money on defense but who comply more with U.S. political aims. The time has come to prioritize allies’ exertion over control, particularly in Europe.

U.S. policymakers should consider whether in some theaters (Europe, for example), existing non‑U.S. efforts are adequate for protecting U.S. interests. In other regions (East Asia), it is clear that allies are freeloading on U.S. exertions, running risks with their own security and potentially even U.S. interests. Over the past 20 years, as East Asian allies’ defense spending has remained anemic while China’s has increased dramatically, this pathology has gotten worse.⁸⁰

The place for U.S. policymakers to start redistributing defense burdens is in Europe. Russia has no hope of regional hegemony in Europe, and there is little reason to worry about a European superstate becoming a competitor with the United States. Even in Asia, however, there is room for sowing uncertainty, demanding more, and forcefully committing to do less.

Some may suggest that the danger in U.S. distance or withdrawal from its alliances is that its allies will not defend themselves as effectively as U.S. commitments can defend them. There is, of course, no certainty that former U.S. allies, or allies with less U.S. leadership, will make exactly the choices Washington would like them to make. But in general, we live in a balancing world, not a bandwagoning world.⁸¹ States jealously guard their autonomy and are more likely to balance against a potential aggressor than to bandwagon or align themselves with it while hoping for the best. The implications are that, as Kenneth Waltz wrote, “others may have to worry about the credibility of our commitments, but we don’t. Our credibility is their problem, not ours, although … many American leaders put the problem the wrong way around.”⁸²

The United States has been the primary security provider in all of its alliances for decades. The level of security the United States enjoys means that U.S. policymakers should play harder to get with their allies. Every ally has more to lose from a U.S. withdrawal than the United States does. U.S. taxpayers, and potentially U.S. servicemembers, deserve a level of effort commensurate with their own interests. Unless policymakers force this issue on U.S. allies, they are unlikely to do more, meaning that Uncle Sucker will continue to deserve the nickname.

Logan, Justin. “Uncle Sucker: Why U.S. Efforts at Defense Burdensharing Fail,” Policy Analysis no. 940, Cato Institute, Washington, DC, March 7, 2023.