For decades, Washington has assumed that military aid translates into political influence. If the United States provides the weapons, intelligence, training, and diplomatic backing that keep an ally fighting, conventional wisdom suggests it should also have considerable leverage over when, and how, that war ends.
Yet, a sweeping new analysis published by the Brookings Institution and authored by Dr. Dafna Rand, a senior fellow at Brookings, the Federation for American Scientists, and the Council on Foreign Relations, argues that the opposite has increasingly become true.
Whether in Ukraine, Gaza, Yemen, or Afghanistan, the U.S. has repeatedly discovered that sustaining an ally’s war effort is often far easier than steering its ultimate direction. Instead of conclusive victories followed by lasting peace, modern conflicts are increasingly settling into drawn-out stalemates, frozen conflicts, or recurring cycles of violence that resist outside pressure—even from Washington.
Dr. Rand’s report examines one of the defining strategic dilemmas confronting American foreign policy in the 21st century: why the world’s most powerful military and diplomatic actor has struggled to shape the decisions of partners whose war efforts depend heavily on U.S. support.
Drawing on more than 30 interviews with senior American officials involved in decision-making throughout four major conflicts, alongside hundreds of government documents, the analysis shows recurring patterns that appear independent of geography or the adversary involved.
“Wars, whether between or within states, are not ending in the 21st century,” Dr. Rand writes. “Frozen conflicts, on-again-off-again fighting, and stalemates have become the norm.”
Dr. Rand argues that this changing nature of warfare has profoundly changed the assumptions underpinning American security strategy.
Following the costly wars in Iraq and Afghanistan, Washington increasingly shifted toward supporting partners rather than committing large numbers of U.S. troops directly to combat. The expectation was that supplying allies with military assistance would provide the United States with considerable influence over battlefield strategy and political consequences.
Instead, Dr. Rand says that American leverage consistently diminishes as conflicts drag on.
One of the study’s central conclusions is that Washington and its partners frequently begin wars without agreeing on what victory actually means. At the outset of each conflict examined—including Ukraine’s defense against Russia, Israel’s campaign against Hamas, the Saudi-led intervention in Yemen, and America’s withdrawal from Afghanistan—American and partner governments shared broad objectives, though often failed to establish detailed political end states.
That omission, Dr. Rand argues, becomes increasingly costly as wars continue.
Early battlefield success frequently encourages partners to pursue more ambitious goals than originally envisioned. At the same time, Washington gradually becomes more interested in negotiated settlements as financial costs mount, domestic political support declines, and wider strategic priorities begin competing for attention.
According to Dr. Rand, many officials interviewed expressed regret that these conversations about political objectives, postwar governance, and acceptable settlement terms did not occur before military campaigns gained momentum.
The report also highlights an uncomfortable reality of modern alliances. Although the United States provides enormous military assistance, it does not exercise command over allied governments or their armed forces. As a result, disagreements naturally emerge over strategy, operational design, and acceptable risks.
Ukraine provides one of the clearest examples. Initially, Washington and Kyiv shared an overriding objective of preventing Russia from conquering the country. However, over time, American officials became increasingly divided over whether continued fighting or eventual negotiations better served long-term U.S. interests.
Some officials viewed prolonging the conflict as strategically beneficial because it weakened Russia’s military while strengthening Ukraine’s defense capabilities. Others believed diplomatic attempts should have begun earlier, particularly after Ukraine’s battlefield gains in 2022 created what they viewed as an opportunity to negotiate from a stronger position.
Dr. Rand notes that internal disagreements within the U.S. government complicated communication with Ukrainian leaders, in particular regarding expectations for territorial objectives and the role military offensives were intended to play in eventually creating conditions for diplomacy.
The Gaza conflict exposed a different, but related, collection of challenges.
Following Hamas’ October 7, 2023, attacks, President Joe Biden’s administration moved rapidly to reassure Israel of unshakable American support while simultaneously urging restraint based on lessons learned from America’s own post-9/11 military campaigns.
Dr. Rand concludes that Israeli leaders largely heard the reassurances while failing to fully internalize Washington’s accompanying warnings about civilian casualties, operational design, and the long-term strategic consequences of an extended campaign.
As the war progressed, American officials increasingly concluded that humanitarian concerns and mounting civilian casualties were not exclusively moral issues but strategic ones as well, arguing that prolonged destruction could ultimately strengthen Hamas’ long-term recruitment and undermine Israel’s own security objectives.
Despite this growing divergence, the report suggests Washington hesitated to use its available leverage aggressively, partly because of domestic political sensitivities surrounding support for Israel.
Another recurring finding centers on American public opinion.
Support for allies often begins overwhelmingly strong immediately after major attacks or invasions. But that support steadily erodes as wars lengthen, casualties mount, humanitarian problems increase, or questions come up regarding the conduct of partner governments.
Dr. Rand says this pattern appears across Yemen, Afghanistan, Gaza, and, increasingly, Ukraine.
Importantly, she argues this erosion can occur even when Americans continue believing the underlying cause remains just. Instead, fatigue over prolonged commitments, concerns about costs, or doubts regarding the likelihood of decisive success gradually reshape political calculations in Washington.
Those changing domestic dynamics, in turn, reduce America’s leverage abroad.
Once congressional debates begin questioning military assistance or public enthusiasm declines, allied governments recognize that Washington’s ability to maintain long-term support has become less certain.
Dr. Rand argues this weakens American bargaining power precisely when policymakers most need it.
Among the study’s most significant recommendations is that future administrations should treat leverage as a rapidly diminishing resource.
Rather than assuming influence will expand alongside continued military assistance, Dr. Rand contends the opposite usually occurs. The strongest opportunity to shape an ally’s political objectives exists during the opening weeks of conflict, before battlefield realities, domestic politics, and diverging national interests begin pulling partners in different directions.
To address this, the report proposes forming formal “security contracts,” or a memorandum of understanding, early in future conflicts that clearly define shared political objectives, expected end states, standards for humanitarian conduct, and mechanisms for periodically reassessing strategy.
Dr. Rand also recommends keeping consistent communication across the entire U.S. national security apparatus, warning that mixed signals from different agencies make it easier for partners to ignore American advice or exploit disagreements inside Washington.
Perhaps most notably, the report argues that future administrations should not focus solely on influencing allies. Even in conflicts involving close partners, Washington should simultaneously pursue diplomatic means with adversaries whenever possible, recognizing that negotiated settlements often require engaging both sides rather than relying exclusively on pressure directed at friendly governments.
Ultimately, the analysis shows that the challenge confronting U.S. policymakers goes beyond any single conflict. As interstate wars, civil wars, and proxy wars become increasingly protracted, America’s ability to translate military assistance into political influence may continue shrinking unless it fundamentally rethinks how partnerships are managed from the very beginning of a war.
“The United States must be brutally honest with its partners,” Dr. Rand writes. “The United States must recognize that pressuring its partners to end wars will get harder, not easier, as time passes and the partner grows better able to resist U.S. pressure.”
Study: Dr. Dafna H. Rand, Why can’t the United States end allies’ wars?, Brookings Institution Foreign Policy at Brookings (2026).
Tim McMillan is a retired law enforcement executive, investigative reporter and co-founder of The Debrief. His writing typically focuses on defense, national security, the Intelligence Community and topics related to psychology. You can follow Tim on Twitter: @LtTimMcMillan. Tim can be reached by email: tim@thedebrief.org or through encrypted email: LtTimMcMillan@protonmail.com