The US emerged as the principal guarantor of global security after World War II and, by constructing a liberal system built on alliances, multilateral institutions, and collective norms, established the international order. The role has been diminishing, especially under the Trump 2.0 administration, as indicated by the 2025 US National Security Strategy (NSS), changes in US strategic doctrines, perceptions of the international community, reactions of allies and adversaries and the growth of alternative security arrangements.
The NSS marks a decisive shift from global stewardship to an “America First” policy that prioritises US interests over shared values, relies on transactional ties, takes a selective approach, demands greater burden-sharing, and avoids open-ended commitments. The US has withdrawn from key multilateral organisations and agreements, such as the Paris Climate Accord and the World Health Organisation, and has been unwilling to bear the institutional and financial burden of leadership. This is not isolationism, but a rethinking of leadership that emphasises unilateral action, economic pressure, and selective engagement. It is redefining alliances such as NATO to be conditional, demanding more burden sharing while simultaneously undermining the predictability and credibility of its commitments. The US has shown a willingness to act unilaterally, as seen in targeted strikes in Syria, Iran and its actions in Latin America, simultaneously reluctant to commit forces in protracted conflicts, resulting in a more transactional and less predictable type of leadership.
The Trump 2.0 strategy is most visible in its approach to alliances. European allies have been alarmed by the US’s lack of certainty about its commitment to NATO, with public statements that have left Article 5 in doubt. The US approach towards Russia, and the dispute over burden sharing in the Ukraine war, have prompted calls for European “strategic autonomy.” The US still has considerable capabilities, including nuclear deterrence and rapid deployment, but the credibility of these guarantees is increasingly in doubt.
The Trump 2.0 administration’s call for NATO allies to spend more on defence, fears it would pull troops out of Germany, and murky statements about obligations under Article 5 have damaged trust in the US alliances. Similar dynamics in East Asia, where US demands for higher host-nation support payments to offset the expense of stationing US forces in South Korea and Japan have stressed the relationship. The US is increasingly treating relationships as a cost-benefit equation as opposed to an end in itself. This has raised uncertainty among allies as to whether the US would respond decisively to aggression.
The rise and assertiveness of China in the South China Sea have exposed the vulnerabilities of the US-led regional system. Washington has stepped up security cooperation with Japan, Australia and India, but there remain doubts over the US’s willingness to confront China in a crisis. Ambiguity regarding Taiwan and mixed signals on regional commitments have generated uncertainty.
Result of US withdrawal
The US has withdrawn from several global institutions and agreements. The decision to withdraw from the Paris Climate Accord, the Trans-Pacific Partnership (TPP) and the World Health Organisation is symptomatic of a wider cynicism about international cooperation. The retreat has damaged US moral authority and its ability to shape global norms, and has opened up space for other actors, especially China, to exert more influence. The US withdrawal from multilateralism undermined the institutional underpinnings of international security. The US reluctance to support international organisations has led to a more fragmented and unpredictable world order.
Rivals are testing the limits of American commitments. The Ukraine war, the confrontation with Iran and its consequences in the region, and the aggression of China in maritime disputes are exploiting perceived US hesitancy. These policies continue to weaken the international order and encourage revisionist agendas. The US must walk the tightrope between domestic regeneration and foreign responsibility. Restoring trust between allies, clarifying obligations and investing in global organisations can mitigate retrenchment. Allies should continue to build capabilities and promote regional cooperation.
The US’s declining role as the world’s net security guarantor is a consequence of strategic recalibration, domestic constraints and shifting global power dynamics. The repercussions of this retreat are serious: it undermines deterrence, encourages adversaries, and challenges the institutional and normative underpinnings of global security. While the US remains a powerful actor, its willingness and ability to underwrite world order are no longer assumed. The future hinges on how the US and its alliances and adversaries react to this new reality. It will also matter whether new forms of partnerships can maintain a stable and peaceful world order.
