The Trump administration has signaled the possibility of retrenchment (including through the reduction of U.S. military forces deployed on allies’ territory), but evaluating whether it serves U.S. interests involves considering a variety of effects. RAND researchers analyzed one aspect of this broader calculation: how retrenchment affects the behaviors of U.S. allies. To do so, they studied historical cases of U.S. retrenchment from West Germany, South Korea, Japan, and Taiwan in the 1960s and 1970s.

Anticipating Allies’ Responses to U.S. Retrenchment

Lessons from Limited Military Withdrawals During the Cold War

Miranda Priebe, Mina Pollmann, Naoko Aoki, Alexandra T. Evans, Kristen Gunness, Garrett Hinck, Samuel J. Leiter, Clara de Lataillade, Nathan Waechter, Nathaniel Edenfield, et al.

ResearchPublished Jul 8, 2025

During U.S. President Donald Trump’s second term, his administration has been signaling the possibility of U.S. retrenchment from Europe (and possibly other regions) to promote allied burden-sharing. Evaluating whether such a change serves U.S. interests involves considering a variety of effects, including the behaviors of U.S. rivals, regional stability, and U.S. defense budgets. RAND researchers analyze one aspect of this broader calculation: how retrenchment affects the behavior of U.S. allies. To do so, they consider lessons from cases of U.S. retrenchment from West Germany, South Korea, Japan, and Taiwan in the 1960s and 1970s.

The United States has long viewed itself as a global security leader, so it has not entirely retrenched from key regions. Still, the United States has engaged in limited retrenchment, which means reducing (but not eliminating) U.S. military involvement in a country or region by withdrawing U.S. forces, downgrading U.S. commitments to allies or partners, or providing less military assistance. Contemporary proponents of limited retrenchment argue that it would incentivize U.S. allies to do more for their own defense, moderate their ambitions, and act in ways that promote regional stability. However, these arguments run counter to the central tenets of post–Cold War U.S. grand strategy. To evaluate these competing beliefs, RAND researchers assessed how these historical U.S. force drawdowns and accompanying policies affected the perceptions and behaviors of these four U.S. allies, including effects on nuclear proliferation.  

Key Findings

  • Allies’ first responses were to attempt to prevent, limit, or shape U.S. retrenchment.
  • Fears of U.S. abandonment led the most vulnerable ally to initiate a nuclear weapon program, but the United States was still able, with difficulty, to convince South Korea to stop its program.
  • Allies did not shift alignment away from the United States or bandwagon with threatening powers.
  • Allies doubled down on their relationship with the United States to preserve what they could of the U.S. commitment.
  • Allies moderated their ambitions or policies toward their rivals.
  • Effects on burden-sharing were uneven. Each ally’s level of vulnerability and economic conditions affected how much it invested in its own defense.
  • Some allies sought to deepen ties with alternative partners, but differing threat perceptions and alignment preferences limited these relationships.
  • Limited U.S. retrenchment did not have a consistent effect on allies’ purchases of U.S. military equipment.

Recommendations

  • Policymakers considering retrenchment should develop a plan to manage allies’ opposition to retrenchment while still incorporating their input about implementation.
  • Policymakers considering retrenchment should expect limited retrenchment’s effect on burden-sharing to be uneven.
  • Policymakers considering retrenchment should decide how to weigh nonproliferation against burden-sharing goals.

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Priebe, Miranda, Mina Pollmann, Naoko Aoki, Alexandra T. Evans, Kristen Gunness, Garrett Hinck, Samuel J. Leiter, Clara de Lataillade, Nathan Waechter, Nathaniel Edenfield, and Karl P. Mueller, Anticipating Allies’ Responses to U.S. Retrenchment: Lessons from Limited Military Withdrawals During the Cold War. Santa Monica, CA: RAND Corporation, 2025. https://www.rand.org/pubs/research_reports/RRA739-8.html.
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