The timing of James Mattis’s resignation as Secretary of Defense may be as significant as the particulars cited in his letter announcing it. It came on the heels of President Donald Trump’s announcement that U.S. troops would be swiftly removed from Syria, and amidst rumors that a similar withdrawal was in the offing for Afghanistan. Trump’s Syria decision alone might have proved the last straw, but there have been countless other occasions since January 2017 when Mattis might have taken a stand on principle. Why this decision? And why now?

Mattis’s resignation letter mentions neither Afghanistan nor Syria, but hints indirectly at both: “the 29 democracies…fighting alongside us following the 9–11 attack on America” and the “the Defeat ISIS coalition” that supposedly includes 74 countries. A “core belief,” Mattis explained, “is that our strength as a nation is inextricably linked to the strength of our unique and comprehensive system of alliances and partnerships.” 

One could be forgiven for questioning Mattis’s claim that he shares President Trump’s view that “the United States should not be the policeman of the world.” The Defense Department that he presides over, and the National Defense Strategy that he issued, is clearly oriented around the defense of others. It reflects a belief, widespread among the U.S. foreign policy establishment, that the U.S. military exists not merely to defend “these States” named in the Constitution, but the plethora of allies, both formal and informal, who have grown dependent upon American military power. It is a subtle, but critical, point of difference between the Founders’ intentions and U.S. foreign policy as it is practiced today. 

And Mattis clearly sees U.S. military power as the bedrock of America’s global influence, more important even than our dynamic economy or our vibrant political culture. Don’t be fooled by his comment, oft repeated in the media, that a failure to properly fund the instruments of diplomacy would result in him having to “buy more ammunition.” The U.S. military bought many more bullets, and ships, and planes, under Mattis’s tenure. If he felt so strongly that the nation’s priorities were out of whack, he would have spent more time challenging the premises that have U.S. forces deployed in over 800 military facilities over the world, fighting wars in at least seven different theaters, and under dubious authority. Instead, he has boasted of securing for the Pentagon enormous spending increases. He even prevailed on the president to endorse a $750 billion Pentagon budget for the next fiscal year, mere weeks after Trump had said $700 billion was much too high (“crazy” even). 

The U.S. military is expensive because the U.S. military is busy. Very busy. It isn’t obvious that this high level of activity advances U.S. security and prosperity. And U.S. promises to defend others allows them to underspend on their militaries. Indeed, that was always the object. It is incumbent upon Mattis — and all those who so loudly lament his departure — to spell out how the U.S. military would be more busy if it wasn’t mostly in the business of defending others from threats that they can and should address themselves.

It is hard to imagine how that is possible. Rep. Ro Khanna (D‑CA) recently tweeted, citing evidence compiled by Stanford’s David Kennedy, “that from 1945–1973 the U.S. had 19 overseas deployments. Since then we have had over 144.” This tracks with evidence that the Congressional Research Service compiled in October 2017. According to the CRS study, explains Cato’s John Glaser, “the United States has engaged in more military interventions in the past 28 years than it had in the previous 190 years of its existence.” Glaser’s back-of-the-envelope calculations count 199 interventions from 1798 to January 1989 and 213 from 1989 to today. He continues: “About 46 percent of Americans have lived the majority of their lives with the United States at war. Twenty-one percent have lived their entire lives in a state of war.”

There may have been occasions when Jim Mattis successfully fended off President Trump’s inclination to use the U.S. military even more often than he did. Reports of attacks thwarted or shelved, including against North Korea and Venezuela, remind that Mattis certainly doesn’t hold the title as the Trump administration’s most bellicose player. But his decision to walk away from the administration on the occasion of the president’s decision to draw down U.S. involvement in two protracted conflicts speaks volumes.