One of the stated goals of U.S. nuclear weapons policy has been to extend deterrence to over 30 U.S. "allies and partners" and assure these countries that the United States will come to their aid, including potentially by using U.S. nuclear weapons, if they are attacked. The 2010, 2018, and 2022 Nuclear Posture Reviews (NPRs), which are periodic executive branch assessments of U.S. nuclear policy, argued for strengthening extended deterrence and posited that it supported U.S. nuclear nonproliferation goals. The 2026 National Defense Strategy did not explicitly mention extended deterrence, instead stating that allies and partners would "take primary responsibility" for their own defense with "critical but more limited U.S. support."
Some Members of Congress have expressed concerns about the Trump Administration's commitment to extend deterrence to U.S. allies and about some allies' potential interest in acquiring nuclear weapons (so-called "friendly proliferation").
Since the beginning of the Cold War, as part of its participation in NATO's collective defense commitment enshrined in the 1949 North Atlantic Treaty, the United States threatened to use military force, including the first use of U.S. nuclear weapons, in response to an act of Soviet armed aggression against Western Europe. Such limited U.S. nuclear use carried the possibility of escalation to an all-out nuclear war between the United States and the Soviet Union; U.S. policymakers deemed this a credible deterrent of potential Soviet attack. The United States also eventually provided assurances to several allies in Asia that it would back their security with U.S. nuclear weapons.
Since the late 1950s, successive U.S. Administrations have expressed concerns about the security threats posed by the possible spread of nuclear weapons since such proliferation could pose a challenge to U.S. national security. During the negotiations on the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) in the 1960s, several U.S. allies sought additional U.S. security assurances while pledging that they would not develop nuclear weapons. U.S. policy has thus sought to extend the U.S. "nuclear umbrella" over allies in Europe and Asia in part as a means to reduce the incentive for them to acquire their own nuclear weapons.
Policymakers and experts in allied countries may debate the extent to which U.S. official statements, capabilities, and plans to defend them constitute a credible security commitment. If an allied government doubts the U.S. extended deterrence commitment, that government may respond by requesting additional U.S. security assurances or by improving its own perceived security through other means. These means may include the development of independent or cooperative nuclear weapons capabilities, or the pursuit of so-called "nuclear latency," which generally refers to a state possessing the technical means to develop nuclear weapons capability. Officials and experts in some states may publicly discuss the desire to acquire their own nuclear weapons, but may not have the requisite infrastructure, materials, or personnel. Such proliferation may also be contrary to their NPT obligations.
During the Cold War, the United States deployed various nonstrategic nuclear weapons, including capabilities that later were eliminated as part of U.S.-Soviet arms control and unilateral commitments, to allied countries. After the end of the Cold War, the United States reduced its nuclear forces, including those stationed abroad, and narrowed the range of contingencies for which it would consider the use nuclear weapons, though it did not adopt a "no first use" policy. The 2010 and 2022 NPRs, which articulated a reduced role for nuclear weapons in U.S. military planning, also emphasized the importance for extended deterrence of U.S. and allied nonnuclear capabilities, such as theater missile defense, and the forward presence of U.S. conventional forces.
The United States extends nuclear deterrence to its allies through forward-deployed nuclear weapons, U.S.-based aircraft capable of conventional or nuclear missions that could be deployed in a crisis, and strategic nuclear forces. The primary stated purpose of U.S. regional nuclear deterrence capabilities has been to deter the limited use of nuclear weapons by Russia, the People's Republic of China (PRC), and North Korea, and those countries' nuclear coercion of U.S. allies and partners. Regional nuclear deterrence systems include the following:
U.S. officials may debate the role of alliances in U.S. strategy. In a 2023 congressional hearing, former U.S. officials stressed the importance of tending to the "software" of ally and partner assurance in addition to the "hardware" of U.S. capabilities. Such "software" efforts include declaratory policy by U.S. leaders, joint planning and close consultations, and exercises that enable allies to ascertain the credibility of U.S. defense commitments, including the potential U.S. use of nuclear weapons.
According to NATO, "nuclear weapons are a core component of [the Alliance's] overall capabilities for deterrence and defense, alongside conventional and missile defense forces." U.S. strategic nuclear forces and independent U.K. and French strategic nuclear forces are described by NATO as the "supreme guarantee" of the security of NATO's 32 member states. (For more, see CRS Insight IN12566, NATO's June 2025 Summit in The Hague.) The United States deploys conventional forces and forward-deploys nuclear weapons for DCA delivery. The United States also has an agreement with the United Kingdom on military nuclear cooperation.
NATO has sought to strengthen its deterrence capabilities since Russia's 2022 invasion of Ukraine. Beginning in 2025, some NATO allies have sought additional arrangements to provide for their security. In May 2025, Poland and France concluded a defense agreement. In July 2025, the United Kingdom and France signed the Northwood Declaration to "deepen their nuclear cooperation and coordination." In August 2025, Germany and France agreed to start a "strategic dialogue" on nuclear issues. Officials in some other NATO countries, including Canada and Sweden, have debated nuclear weapons issues.
U.S. allies Japan, South Korea (officially the Republic of Korea, or ROK), and Australia have expressed concern about changes in PRC and North Korean nuclear weapons and other capabilities. The United States maintains conventional military forces in Japan and South Korea, as well as elsewhere in the region, but it no longer forward-deploys nuclear weapons there. The 2018 NPR and Biden Administration officials have posited that SLCM-N would seek to deter adversaries and assure allies in the region.
In 1960, the United States signed a mutual defense treaty with Japan. The United States and Japan regularly engage and conduct alliance and defense cooperation, including through the Extended Deterrence Dialogue. (See CRS In Focus IF10199, U.S.-Japan Relations.)
In 1953, the United States signed a mutual defense treaty with the ROK. Following the 2023 Washington Declaration, the United States and the ROK created a Nuclear Consultative Group. (See CRS In Focus IF10165, South Korea: Background and U.S. Relations.)
Recently, officials in Japan and the ROK have publicly discussed nuclear weapons issues. Both governments continue to reaffirm that they do not seek their own nuclear weapons and support the strengthening of extended deterrence including through trilateral cooperation.
In 1951, the United States signed a mutual defense pact (ANZUS) with Australia and New Zealand. In the 1980s, the United States suspended its defense commitments to New Zealand following changes to New Zealand's policies on nuclear weapons. The U.S. and Australia's mutual defense relationship continues; the two countries conduct a Strategic Policy Dialogue. (See CRS In Focus IF10491, Australia: Background and U.S. Relations.)
The United States has bilateral defense commitments with other countries that may or may not be included in the NPR's "allies and partners" formulation for extended nuclear deterrence. The United States has an unofficial but robust relationship with Taiwan; the 1979 Taiwan Relations Act (P.L. 96-8) creates "strategic ambiguity" about potential U.S. actions in the event of a PRC attack on Taiwan. (See CRS In Focus IF12481, Taiwan: Defense and Military Issues.)
Congress provides authorization and appropriation of funds, as well as oversight of U.S. government programs relevant to U.S. extended deterrence policies. The Senate considers providing advice and consent to ratification of treaties negotiated by the executive branch. Some Members of Congress also directly engage with leaders in U.S. ally and partner countries. Through intelligence community briefings and other oversight activities, Congress may track changes in military capabilities of regional adversaries, including Russia, PRC, North Korea, and Iran, and assess potential development of nuclear weapons by other countries, including U.S. allies and partners.
Congress may oversee, including through hearings with executive branch officials and outside experts, U.S. engagement with allies and partners, including efforts to assure allies and partners of the credibility of U.S. defense commitments. The 2023 report of the Congressional Commission on the Strategic Posture of the United States (Strategic Posture Commission, or SPC) argued that "any major change" to U.S. strategic policy or posture should be "predicated on meaningful consultations" with allies.
Congress may oversee the executive branch's assessment of the ways in which U.S. nuclear weapons fit into the overall mix of U.S. capabilities in regional security architectures. Some U.S. allies and partners in the Euro-Atlantic and the Indo-Pacific may request changes to existing U.S. extended nuclear deterrence commitments; U.S. allies and partners in the Middle East and elsewhere may also request the protection of a U.S. "nuclear umbrella."
Some Members of Congress cited concern about the potential insufficiency of U.S. regional nuclear capabilities when Congress required the U.S. Navy to start up the SLCM-N program. Congress may continue to oversee U.S. programs to modernize relevant U.S. nuclear and nonnuclear capabilities. Members of Congress may debate investments in, and deployment of, such capabilities.