However, one of the clear lessons from Afghanistan is that NATO is unable to execute operations without U.S. leadership. Ultimately, the level of Western support for Ukraine—and its effectiveness—will rise and fall based on U.S. policy and commitment, just as it did in Afghanistan. A U.S. policy of support to Ukraine remains the biggest lever to stop Russia’s aggression and ensure Ukrainian victory.

During 20 years in Afghanistan, NATO institutions’ most important contribution was coordinating allied and partner military personnel support. Because of caps on total U.S. personnel in country, contributions in areas such as force protection for NATO member states and partners such as Georgia allowed the U.S. to deploy more higher-end forces and thereby increase overall mission effectiveness. At the peak in January 2011, non-U.S. participants made up 42,000 of the 132,000 deployed, while by the end of the mission in 2021, there were 7,100 allied and partner troops and 2,500 U.S. personnel in country. Allies and partners also suffered a heavy burden of casualties even with smaller numbers of total personnel: 1,144 killed in the war as compared to 2,465 from the United States.  

NATO also contributed financially, but significantly less than the United States: the NATO Afghan National Army Trust Fund contributed a total of $3.4 billion from 2007 to 2021, while obligations from the U.S. Afghanistan Security Force Fund totaled $74.7 billion from 2005 to 2020. Still, the Trust Fund demonstrates how NATO can provide a trusted venue for non-NATO partner countries to contribute—South Korea donated $319 million, for example. It also shows how NATO processes and standards enable small nations’ efforts to build into larger contributions. 

While NATO formally uses the decision process of unanimity, U.S. policies dominated the trajectory of NATO’s mission in Afghanistan. At each critical juncture of the mission—the early days after the 9/11 attacks, the expansion of the mission in 2006, the 2009-2011 surge, and the final departure in 2020-2021—the record of debate followed the same pattern: The U.S tended to inform allies of decisions, which then became alliance policy, rather than bringing allies into the decision-making process.

Perhaps the most striking example was in the 2020 U.S.-Taliban agreement, where the U.S. committed to withdraw allied and partner troops—even though NATO was not a party to the agreement. Key allies, including the UK, criticized the U.S. policy, and others might have preferred to continue the mission. But as Secretary General Stoltenberg later explained, allies’ decision to agree to the departure “reflects the reality that when the United States decided to end its presence in Afghanistan…there was no willingness from other European allies, Canada, or the partner nations, to replace or to fill in after the United States.” 

The biggest lesson therefore for Ukraine is that NATO, at least in its current configuration, cannot conduct substantial operations in the absence of policy leadership from the United States. There are several factors that limit the non-U.S. allies’ influence, but greater and more focused U.S. resource investment is probably the most important. Even though overall European contributions to Ukraine exceed those of the United States when budgetary and humanitarian assistance are included, U.S. military assistance exceeds that of all EU members combined.  

European members of NATO have struggled to provide Ukraine with sufficient military assistance due to slow progress in expanding their defense industries. NATO’s ability to contribute military forces as it did in Afghanistan is also less relevant in Ukraine, where the most important lever is probably materiel assistance. Some allies have provided new capabilities before the United States, such as the UK and France providing Storm Shadow and SCALP long range missiles. However, Germany’s decision to delay sending Leopard tanks until the United States provided Abrams illustrates how U.S. policy remains a key limiting factor.

Even if European countries were able to step up with more materiel, their dependence on the U.S. military goes deeper than procurement budgets. The United States has often launched simultaneous missions with more expansive mandates side-by-side with NATO-led operations. After 2014, for example, the NATO-led Resolute Support gave up its combat role, but U.S. Forces-Afghanistan, led by a dual-hatted U.S. general, continued to have a combat mission. 

In Ukraine, the U.S.-led Security Assistance Group will probably maintain a more involved operational role overseeing “the full-spectrum of security assistance” than a NATO command focused on coordinating training and sustainment. In planning new operations and strategies, the smaller policy and planning offices of the European defense ministries also face coordination challenges, and cannot match the U.S. Defense Department’s depth of expertise.

The experience in Afghanistan does show the benefits a NATO-led operation can provide. NATO is uniquely good at coordinating security assistance from many countries. NATO’s deliberate decision-making rhythm may also bring a longer-term perspective. U.S. policymakers set overly high expectations for the 2023 Ukrainian counteroffensive, in part because of accurate concerns about declining U.S. support. If NATO can bring a longer-term approach, that would be welcome.

NATO’s new effort on Ukraine will hopefully lead to larger and more coherent support. But the idea that NATO can somehow substitute for U.S. disengagement is flawed, as the record of NATO’s engagement in Afghanistan clearly demonstrates. As one joke goes, the acronym NATO also stands for “need Americans to operate.” Ensuring an ambitious and coherent U.S. policy and strategy to support Ukraine’s victory remains as important as ever. 

Andrew Radin is a senior political scientist at RAND, a nonprofit, nonpartisan research institution. From 2018 to 2020, he served as a country director for Afghanistan in the Office of the Under Secretary of Defense for Policy.