What Are Allies Good For, Anyway?

The relationships that Trump takes for granted matter.

Winston Churchill, Franklin Delano Roosevelt and Joseph Stalin at the Yalta Conference, February 1945. (Photo by Hulton Archive/Getty Images)

As a candidate and then as president, Donald Trump has criticized and complained about U.S. allies—and especially about the amount of money that they pay toward their own defenses. And it hasn’t all been talk: His administration recently announced a major reduction in the number of U.S. forces in Germany. (“We don’t want to be the suckers anymore,” he said.) Reports claim that South Korea may be next.

As has so often been the case with the Trump administration, the president’s words and deeds force us to go back to basics—to understand and make the case for norms and practices that he has ignored or rejected. So let’s try to answer a simple question: What are allies and what do we need them for?

First, some background. For most of history, alliances were situational and short-term, like the two Grand Alliances formed to halt the expansionism of France under Louis XIV, or the series of coalitions formed to defeat Napoleon. Outside of wartime, alliances tended to be unbalanced, and they were not necessarily friendly and consensual: There was the exploiter and there was the exploited. Participation in regional—and later global—hegemonic orders used to be more forcible than voluntary, and usually the hegemon benefited in a mercantile sense while the subjects received protection. Only in the nineteenth century did a world power—the United Kingdom—for the first time use its hegemony to liberalize trade to benefit all participants. In time, the United States would take on that responsibility, and expand upon it.

One indicator of how historically anomalous the U.S.-led world order since 1945 has been is the fact that some U.S. allies ask, or even beg, the United States to house its troops in their countries. The United States has only reluctantly accepted this responsibility—and that reluctance is itself part of what has made U.S. global leadership appealing to much of the world. As Robert Kagan notes in his 2012 book The World America Made, never in history have small powers been so desirous of having a great power station troops within their borders, never in history has a great power been so reluctant to accept this invitation, never in history has a great power been so forceful in asking smaller powers to spend more on military capabilities, and never in history have smaller powers been so resistant to such a request.

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Now on to the question of what allies are good for. First, there is the obvious answer: They increase the aggregate military power of their bloc. This is what Trump has been complaining about for years—that some of our allies don’t pay as much as they ought to for their own defenses, and so don’t do enough to increase the alliance’s aggregate military power. On this point, he is not factually wrong. (There often are, though, good reasons to think twice before asking allies to pay more.) Nor is he the first president to push NATO allies to spend more; his two predecessors did as well.

But increasing aggregate military power is not an alliance’s only benefit—nor necessarily the most important one. Allies also provide each other with geographic access and knowledge. The United States is unlikely to have to fight a land war in its home territory. But if the United States ever needs to fight another war in Europe, the current presence of U.S. troops allows the United States not to have to worry about having to lead another Normandy invasion. Additionally, this presence helps to acquaint the U.S. military with Europe’s terrain, geography, and climate. And forward deployments of troops to Europe and Asia have created buffer zones between the United States and Russia and the United States and China—in America’s favor. The Russians and the Chinese are not at our doorsteps, but we are at theirs.

Alliances can also legitimize the collective actions of their participants. Americans remember the Iraq War as a unilateral move due to France’s and Germany’s objections. The truth, however, is that a half-dozen other nations participated militarily alongside the United States, and dozens of others joined in other ways. Russia’s unilateral actions in Georgia in 2008 and Ukraine starting in 2014 resulted in punitive action against it. But American actions in the Balkans in the 1990s, Iraq starting in 2003, Libya in 2011, Pakistan for the past two decades, Yemen in the 2000s, Somalia in the 1990s, and so on, never resulted in any international punitive backlash—sanctions, for instance—in part because those actions were taken alongside allies.

Alliances also share intelligence. Five Eyes is an intelligence-sharing coalition of five English-speaking countries—the United States, the United Kingdom, Canada, Australia, and New Zealand. In Asia, Americans benefit from South Korean intelligence services spying on North Korea. Israel has been a useful intelligence provider to the United States, and not only about Iran and potential threats in the Middle East: In 2015, for instance, it was Israel that informed the National Security Agency about the Russians’ access to the agency’s hacking tool.

By providing our allies with security guarantees, the United States prevents them from—or at least reduces their likelihood of—accommodating our enemies against our interests. Indeed, because of our security guarantees, our allies often go out of their way to accommodate our interests, sometimes even against their own, so they can stay on our good side.

Last but not least, by allowing the forward deployment of the U.S. military, America’s allies make it possible for the United States to resolve what Peter Feaver calls the “civil-military relations problematique”: that Americans needed a large standing army but feared that it would be used to undermine liberalism in the United States. The resolution was forward deployment. Americans got to keep their large Army but far away in somebody else’s country.

Among the anomalies of the U.S. liberal world order is how relatively little the United States, compared with previous hegemonic powers, spends on its military, despite its large responsibilities around the world. From 1960 until the demise of the USSR, the Soviet Union never spent less than 10 percent of its GDP on military expenditures, while occasionally getting close to 20 percent of it.  By contrast, the United States never spent more than about 9 percent of its GDP—which would have been impossible without America’s liberal alliance system.

The United States is lucky to have its many great allies, and they are lucky to have us. Only a fool would choose to endanger the current system.