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.

Wars between states—particularly protracted, high-intensity conflicts (such as the Russia-Ukraine war), which involve the commitment of significant resources—have the capacity to reshape how states fight by providing both the opportunity and the pressure to use and adapt novel capabilities. In this report, the authors closely examine the tactical and operational levels of the fighting in Ukraine to make eight novel or notable observations about contemporary warfighting. These observations include insights about the use of uncrewed aerial and naval systems in combat, the transparent battlefield and the problem of persistent surveillance, the effectiveness of air defenses and electronic warfare against uncrewed systems, the need for low-cost expendable systems in a protracted conflict, the accessibility of commercial space-based assets for military purposes. The authors also use these observations to forecast the character of future wars by evaluating whether and how their observations might translate to two potential U.S.-involved conflict scenarios: a war in Eastern Europe between North Atlantic Treaty Organization members and Russia and a war in the Indo-Pacific between the United States and the People’s Republic of China. The authors conclude by highlighting the implications of their observations and providing recommendations for the Department of the Air Force, the Department of Defense, and U.S. government policymakers.

Improvements in Russian and Chinese counterspace capabilities could endanger the space-based capabilities that the United States relies on for a broad array of military and economic functions. The proliferation of U.S. and adversary capabilities could lead to unstable competition in space, raising the risk of unintended military escalation. In this report, the authors examine the conventional wisdom on escalation in the space domain to offer recommendations for how the U.S. Space Force (USSF) and other stakeholders can better prepare to deter and manage escalation. They investigate the implications of six propositions related to stability: (1) the incentives to employ offensive capabilities early in a conflict, (2) the benefits of leveraging foreign and commercial systems, (3) the utility of communications channels for crisis prevention and de-escalation, (4) the feasibility of promoting shared norms of responsible behavior, (5) the strategic benefits of selective revelation, and (6) the use of reversible capabilities to manage escalation.

A war between the United States and a capable, nuclear-armed adversary would introduce the risk of destruction on a scale the United States has not seriously contemplated since the end of the Cold War. The main debate in the policy world is between advocates of theories of victory that are reliant on denial and advocates of theories of victory that depend on cost imposition. Cost-imposition strategies, such as those requiring a distant blockade or a punitive air campaign, require the United States to successfully navigate what the authors refer to as the Goldilocks Challenge: specifically, identifying with high confidence a “sweet spot” of pressure points that are valuable enough to influence enemy decisionmaking but not so valuable that they cause unacceptable retaliation. To help the U.S. Air Force evaluate the feasibility of a cost-imposition strategy and assess the associated risks of uncontrolled escalation, the authors examine the ability of past decisionmakers to identify adversary thresholds and to apply this information to control escalation during militarized crises between nuclear-armed states. The authors analyze three historical cases of militarized crises and conflicts between nuclear-armed major powers: (1) the 1962 Cuban Missile Crisis between the United States and the Soviet Union, (2) the 1969 border conflict between China and the Soviet Union, and (3) the 1995–1996 crisis between the United States and China over Taiwan.