Sixty years ago Sunday, President Harry Truman ordered U.S. forces into battle to repel North Korean hordes streaming across the 38th parallel in a surprise attack on the South. What Truman termed a “police action,” others have called “the Forgotten War,” overshadowed by the next decade’s bitter controversy over Vietnam.

It’s odd that a conflict as pivotal as the Korean War could ever be “forgotten.” U.S. involvement saved millions of South Koreans from being swallowed up by a militarized slave-state.

That came at no small price: Truman’s unilateral decision crossed a constitutional Rubicon, eroding Congress’s power to declare war and leading to the deaths of more than 36,000 American soldiers — most of them conscripts — without the courtesy of an up-or-down vote on the war.

Americans can be proud of what their sacrifices helped achieve. But the Korean War’s anniversary ought to prompt rethinking a Cold War-era alliance well past its sell-by date.

When America signed a mutual defense treaty with the South after the 1953 armistice, the war-weakened Republic of Korea faced a communist enemy backed by China and the Soviet Union. Today, the “hermit kingdom” to the North remains belligerent — as shown by its recent torpedo attack on the ROK vessel Cheonan — but it’s a desperately poor, internationally isolated basket case.

A look at the famous nighttime satellite photo hints at the two countries’ relative strengths. In the North darkness reigns; but to the South, the brightly lit ROK is the world’s “most-wired nation” and its 13th-largest economy. It has twice the population and more than 20 times the GDP of the North.

Yet today some 28,000 U.S. troops remain in South Korea, ready to defend an ally that’s more than capable of defending itself. After 60 years of guarding the ROK, haven’t we done our part?

Apparently not. In a Saturday press briefing, President Obama marked the war’s anniversary by making clear that the U.S. isn’t going anywhere. He announced that the U.S. would retain wartime command of ROK troops in any future peninsular conflict, scrapping a plan to turn over control of South Korean forces in 2012.

The U.S. has an interest in denuclearizing the Korean peninsula, of course — but that doesn’t require American troops stationed along the DMZ, bearing a disproportionate amount of the risk in an allegedly “mutual” defense pact.

South Korea sacrifices some sovereignty in this bargain, but at least it saves money. The ROK spends 2.6 of its GDP on defense — well less than the United States — and falling. As my colleague Doug Bandow puts it in a forthcoming study, “Americans are borrowing money to pay to defend the South so South Koreans can spend their money on other priorities.”

That’s a common pattern in our Cold War-era alliances. U.S. membership in NATO, an alliance crafted to contain an enemy that collapsed 18 years ago, has helped keep European defense budgets low and subsidize lavish welfare states for NATO members. Yet we still account for half of the world’s military expenditures with a bloated “defense” budget largely devoted to the defense of other nations.

In his first inaugural address, Thomas Jefferson outlined the ideal American foreign policy: “peace, commerce and honest friendship with all nations, entangling alliances with none.” Toward that end, President Obama’s other announcement Saturday, that he would (finally) back a free-trade agreement with South Korea, was at least a half-step in the right direction.

In the years to come, we would do well to move closer to the Jeffersonian ideal in international affairs. One thing is clear: In an era of trillion-dollar deficits as far as the eye can see, America can’t afford to play globocop any longer.