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Biden’s in Europe to reassure nervous allies. When does reassurance work?

Reinforcing alliances is a useful foreign policy tool, research finds

British Prime Minister Boris Johnson, his wife Carrie Johnson, President Biden and first lady Jill Biden walk outside Carbis Bay Hotel, Carbis Bay, Cornwall, Britain, on Thursday. (Toby Melville/Reuters)

As many analysts have noted, President Biden intends to use his visit to Europe this week to reassure nervous U.S. allies, in person, that “America is back.” After four years of President Donald Trump’s open skepticism about the value of U.S. alliances, Biden hopes to reinforce his message that the United States remains committed to their security.

That matters. As I wrote here in March, such gestures serve an important function: to dissuade allies from adopting policies that could reduce their commitment to the alliance, diminish U.S. influence, or trigger regional arms races. My research on alliances suggests that U.S. officials reassure allies with these concerns in mind.

What is reassurance?

Alliance treaties are among the most important ways countries commit themselves to each other’s defense. By putting this commitment in writing, countries can make it costly to nations’ reputations to renege on promises of support.

Reassurance involves reminding allies that these initial promises still hold, and that the United States will deliver protection as promised. Signals of reassurance reinforce alliance treaties by showing that Washington is willing to commit resources on allies’ behalf, to ensure that the United States has the necessary military capabilities nearby, and to further stake its reputation on defending allies.

How do policymakers signal this kind of reassurance? One tool, of course, is deploying U.S. forces to allied territory. This puts American lives at risk and provides capabilities that can be used in a crisis. But while troop levels in allied countries are typically stable in most years, they can also be rapidly changed, leaving allies with concerns about future U.S. troop levels and intentions.

Other signals, such as high-profile diplomatic visits and leader statements, are more symbolic. Yet these gestures create reputational costs and thus credibly signal U.S. commitment to the alliance for the foreseeable future.

Biden has used a mix of these signals already, by canceling Trump’s plan to withdraw 12,000 U.S. troops from Germany and telling officials in allied countries that his administration is recommitting to U.S. alliances. This is consistent with the historical norm; since 1950, U.S. presidents have on average issued eight statements of reassurance to allies each year, and Washington has maintained over 100,000 troops in allied countries.

Biden wants to reassure allies that the U.S. is still interested in their security

Why would the United States reassure its allies?

Allies have good reason to seek reassurance, as circumstances can change over time. New leaders come into power, for instance, or the threat environment shifts. Allies might worry that Washington could eventually terminate the alliance or perhaps even renege on its promise when called to assist. The United States, for example, terminated its formal alliance with Taiwan in 1979, when the United States and China normalized diplomatic relations.

The United States also reassures its allies to discourage them from finding substitutes for the alliance. My research suggests that the United States is more likely to reassure allies that have greater abilities to go their own way, whether by pursuing nuclear weapons, developing military self-reliance or aligning with other countries. Any of these decisions can reduce an ally’s dependence on U.S. protection. This, in turn, diminishes U.S. influence and future bargaining leverage and makes those allies less willing to go along with U.S. preferences.

France, for example, left NATO’s integrated military command in 1966, several years after obtaining nuclear weapons, and only rejoined in 2009. And in response to Trump’s presidency, French President Emmanuel Macron suggested a European army that could allow Europe to become more independent, hedging against U.S. unreliability or bullying on costs. Biden’s commitment to NATO could blunt some of this momentum, though Macron has continued to argue that greater autonomy would insulate Europe from future U.S. policy shifts.

Looking for more info? Check out TMC's topic guide on NATO and European security.

Will Biden’s trip actually reassure allies?

Biden’s desire to reassure allies is no guarantee that his attempts will succeed. Nevertheless, there is evidence that foreign visits and public statements of reassurance do influence their recipients. A number of studies suggest that presidential statements and visits reduce the likelihood that countries receiving them will be targeted for attack and increase the degree of cooperation and harmony in U.S. alliances.

However, Biden’s diplomatic assurances can do only so much. Many allies worry that Biden could be a one-term president, succeeded by leaders whose views align more closely with Trump’s than with Biden’s. More generally, since U.S. resources are constrained both by relatively flat defense spending and by increasing focus on East Asia and competition with China, allies especially in Europe may question whether Washington has the wherewithal to defend them.

Diplomatic signals are only one tool among many at Biden’s disposal. To most effectively reassure allies, the Biden administration could couple its diplomacy with increasing the resources dedicated to defending allies, such as investing in new technologies or weapons systems that can quickly and effectively shield allies from attack or deploy existing capabilities in and near allies’ territories. That would involve trade-offs. Resources are finite, and committing forces or technologies to one region may prompt others to speculate about whether Washington can respond to problems elsewhere.

In other words, the Biden administration is unlikely to reassure every ally completely and will have to decide how to use its time and resources. But as long as the United States hopes to maintain its alliances, U.S. leaders are likely to continue to view reassurance as useful to further American interests.

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Brian Blankenship (@BrianDBlank) is an assistant professor of political science at the University of Miami and a Stanton fellow at the Council on Foreign Relations. His research studies military alliances and U.S. foreign policy.