The Burden-Sharing Dilemma in U.S. Alliances

Editor’s Note: The Biden administration seeks to work more closely with U.S. allies, but this admirable ambition faces many challenges in practice. Brian Blankenship of the University of Miami warns that allies have incentives to do too little when it comes to burden sharing. However, he also cautions that more capable and independent allies will be less likely to heed U.S advice, which poses its own set of dilemmas.

Daniel Byman

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Few aspects of U.S. alliances are as contested as defense burden sharing. While often associated with Donald Trump, U.S. efforts to pressure its allies to assume more responsibility for their own defense are as old as American alliances themselves. President John F. Kennedy, for example, warned in 1963 that the United States “cannot continue to pay for the military protection of Europe while the NATO states are not paying their fair share.”

Efforts to encourage allied contributions are beset by twin challenges. With too little burden sharing, the United States must cover the costs of defense alone or else risk failing to deter adversaries. With too much, Washington risks losing influence over its allies. These challenges present differently in the two primary regions where the United States has formal military alliances: Europe and the Indo-Pacific.

The Burden-Sharing Dilemma

Persuading allies to shoulder more of the costs of defending themselves presents two central challenges. The first is that doing so can fail. Allies may be unwilling to devote scarce resources to defense if they expect that the United States will defend them. Alternatively, allies may not perceive their external threats threat as sufficient to justify these investments.

The second and perhaps more fundamental challenge is the “burden-sharing dilemma.” By assuring allies that it will protect them and thereby implicitly assuming some of its allies’ defense costs, the United States can gain a degree of leverage over them. This can range from influence over allies’ trade policy to their willingness to seek nuclear weapons. The more the United States relies on allies to front the costs of defending themselves, however, and the more allies can fend for themselves, the less easy it is for Washington to persuade them to conduct foreign policy in alignment with its preferences.

The Dilemma in Europe and the Indo-Pacific

These risks are likely to play out differently in Europe and the Indo-Pacific. In Europe, the risk is not so much about the NATO alliance’s ability to produce enough military power to prevent Russia from obtaining regional hegemony. Indeed, few U.S. allies are as well positioned to assume greater responsibility for their own defense as those in Europe. Germany alone has an economy twice the size of Russia’s, which has struggled to invade the much smaller country of Ukraine.

Instead, burden sharing in Europe poses two problems. The first is that the major powers of Western Europe could become sufficiently capable of defending themselves that they then could more easily ignore Washington. This risk is familiar. Many of the continent’s previous attempts to unite on defense involved creating new institutions outside of NATO—and thus less subject to U.S. control. These included institutions designed to facilitate military integration and coordinate defense investments. American officials feared that these efforts would not only undermine U.S. defense exports but also reduce Europe’s willingness to follow the U.S. lead on foreign policy. Indeed, French President Emmanuel Macron has called for creating an independent European army, equipped by European defense manufacturers, to make Europe a “third force” in the world.

The other main risk is that an independent Europe might not defend NATO’s most vulnerable members. Poland and the Baltic countries of Estonia, Latvia, and Lithuania all share borders with Russia and outpace most of their fellow NATO states in both defense spending and aid to Ukraine as shares of their gross domestic product. By contrast, both before and since Russia invaded Ukraine, defense spending has been less promising in the rest of Europe, which generally perceives a lower threat from Russia. In addition, their militaries do not have the capability to rapidly move large numbers of forces or to otherwise defend the most vulnerable states from a sudden Russian attack. Not coincidentally, Poland and the Baltic countries have long been skeptical of European defense efforts, fearing that Western Europe might not defend them, and have instead emphasized defense ties to the United States.

In the Indo-Pacific, by contrast, the primary risk is that U.S. allies alone are not capable of preventing Chinese regional hegemony. Unlike Russia, China is by far the largest economy in its region and has an increasingly capable military to match. Moreover, the United States has only a few formal treaty allies in the region and the formation of a broader coalition to counterbalance China faces hurdles. Forming counterbalancing coalitions faces a free-rider problem, as countries may wish to enjoy the benefits of preventing Chinese expansion while not wanting to pay the costs—either in resources or in Chinese hostility. Indeed, there is little appetite for openly breaking with Beijing, in part because China is the largest trade partner for nearly every country in the region.

Coping With the Burden-Sharing Dilemma

If the United States elects to rely more on allied burden sharing, it will to some extent be forced to cope with these challenges. Indeed, due to strains on scarce U.S. resources, there is some reason to expect that it will.

Some of this scarcity is internal. A combination of inflation, rising debt, and competing domestic spending priorities has made substantial increases in U.S. defense spending unlikely. Adjusting for inflation, U.S. defense spending has been essentially flat since 2010.

But it is also partly external. Three successive U.S. presidents have hoped to shift resources toward the Indo-Pacific to balance against China’s rise. The Obama administration spoke of a “rebalance” to Asia, while the Trump and Biden administrations explicitly cast China as the United States’s primary competitor. A faction of the Republican Party increasingly embraces the Indo-Pacific as the priority region and favors a reduced U.S. role in Europe.

If the United States hopes to lean more on its allies’ contributions while also mitigating the burden-sharing dilemma, one of its most potent tools is conditional pressure: threatening to limit its commitment to defend allies unless they contribute more, and reassuring them that it will defend them if they do. Conditional pressure has two advantages over abandoning U.S. alliances outright. First, conditional pressure runs less risk of emboldening adversaries to behave aggressively. Second, it is less likely to make allies sufficiently desperate that they seek means of achieving security that Washington opposes—such as acquiring nuclear weapons or appeasing U.S. adversaries.

Research suggests that U.S. threats of abandonment can increase allied defense contributions, and that other forms of pressure—such as simply criticizing states that fail to contribute more—are ineffective. During the 1970s, for example, the Nixon administration faced congressional pressure to withdraw U.S. forces from Europe. Nixon successfully encouraged European governments to boost their defense spending by assuring them of his commitment to NATO while warning that Congress might force his hand. By invoking the possibility that congressional pressure or a Trump reelection might similarly jeopardize U.S. alliance commitments, the Biden administration can make the case that sharing more of the burden is allies’ best hope of building goodwill in American domestic politics.

Conditional pressure certainly still comes with risks. Allies asked to assume more of the costs for defending themselves may still elect to go their own way. Moreover, not all allies are likely to be equally responsive. Western Europe, for example, is more insulated from the threat of Russian invasion than are NATO members in Eastern Europe and so may be less responsive to U.S. pressure to increase defense spending.

Whether the United States prioritizes Asia or is willing to accept less control over allies are political choices, not inevitabilities. It may, as in the past, avoid making a decisive shift. In any case, its choices will come with unavoidable trade-offs.