By the end of the first year of President Donald Trump’s second term in the White House, descriptions of systemic crisis in – or even predictions of the end of – the transatlantic security alliance were commonplace. And yet NATO had not only survived, but by January 2026 was taking on new roles and responsibilities – playing a more important role in facilitating continuing western (including US) military assistance to Ukraine, and potentially also with regard to Greenland, and perhaps wider Arctic security. It was certainly true that Trump’s brusque and unpredictable approach to international diplomacy led to some bruising encounters with allies and partners. These proved short-lived, however, and were managed short of inflicting serious or durable damage on the core NATO institution. The analysis here seeks to explain how and why.

*Originally published February 2026. E-International Relations is free to read. We rely on reader support to make this possible.

NATO’s Enduring Institutional Strengths

The 1949 North Atlantic Treaty (NAT) places no automatic obligation on its signatories to offer military assistance to allies under attack. Article 5 merely requires each signatory to take “such action as it deems necessary”, leaving the door open in theory for them to take no enforcement action. Its content nevertheless suggested that signatories wanted something more solid and permanent than a traditional military alliance. There, little or nothing might be done to provide collective military resources, but the wording of the NAT’s Article 3 states that “in order more effectively to achieve the objectives of this Treaty, the Parties separately and jointly by means of continuous and effective self-help and mutual aid, will maintain and develop their individual and collective capacity to resist armed attack” [emphases added]. The treaty also provided for the creation of the intergovernmental North Atlantic Council (NAC), in which each signatory would be represented.    

Nicholas Henderson, a British diplomat involved in negotiating  the NAT, recalled the “overriding presence of … common purpose” animating western leaders at the time. This was institutionalised in agreements by member states in 1952 to create international political and military staffs, and a process for continuously reviewing national defence plans. A seminal 1957 study by Karl Deutsch et al later called this review process “an unprecedented performance” in the degree to which sovereign states opened up their defence planning processes to multilateral scrutiny and recommendation.

Neither the force-planning process nor any other aspect of NATO’s institutional development involved formal supranationalism. There are no legal or institutional means to compel member state compliance with its procedures or recommendations. Nevertheless as they developed, the force-planning process – overseen by a Defence Planning Committee (DPC) – together with wider political and diplomatic consultations in the NAC, increasingly influenced the decision-making of member states. As they did so, NATO ‘matured’ into a significant international security institution. The concept of international institutions is most closely associated with American scholar Robert Keohane, who defined them as “involv[ing] persistent and connected sets of rules (formal or informal) that prescribe behavioral roles, constrain activity and shape expectations” among member states. Drawing on insights from the academic regime theory paradigm, it can also be argued that the development of a ‘consultative regime’ among member states informally but vitally helps regulate and shape the way in which they conceptualise, formulate and implement policies on issues within an institution’s remit.

Historical Challenges to NATO’s Cohesion

During the Cold War, there were few occasions when national governments felt able to ignore collective recommendations from NATO altogether. Even the most powerful members, including the United States, were willing to defer or modify planned reductions in response to intra-institutional pressures. NATO’s consultative and behavioural regimes had developed substantial robustness by the 1980s. Thus, as the scholar Glenn Snyder noted in 1984, “because the alliance itself is fundamentally stable … [specific] policy divergences may develop and persist”.  However Snyder added a caveat: “the alliance is stable because it is essentially a product of the structure of the system and of the common security interests generated thereby. So long as that structure and those interests persist the allies are free to disagree”.

NATO was thus stable within the systemic context of Cold War bipolarity, but would this  survive that order’s demise in 1989-1991? Virtually all member states did make significant defence budget cuts during the 1990s in response to the disappearance of the Soviet threat and the resultant quest for a  ‘peace dividend’. These reductions took place within parameters agreed in NATO however. The established force-planning process, together with the behavioural and consultative regimes surrounding it, were maintained as the key framework for ongoing discussions about force levels and commitments.

Prior to Trump’s first term, the most significant questions posed to NATO’s continued viability came during George W. Bush’s presidency in the early years of the present century. During the 2000........

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