What roles have NATO expansion and EU integration played in the conflict?
Executive summary
NATO enlargement since the Cold War has expanded the alliance from 12 to 32 members and kept the “door open” to European aspirants, a policy Moscow repeatedly cites as a central grievance [1]. EU deepening of defence cooperation and EU–NATO operational ties since 2014 have reinforced Western support structures for Ukraine while also raising debate about strategic autonomy and burden‑sharing within the transatlantic alliance [2] [3] [4].
1. Why enlargement matters: a security architecture reshaped since 1989
NATO’s post‑Cold War expansion brought many former Warsaw‑bloc states into the Alliance and is explicitly presented by NATO as a stabilizing integration of new democracies into Euro‑Atlantic institutions; this expansion—from 12 to 32 members—is central to how European security was reorganized after 1989 [1]. Critics and analysts argue that the expansion changed Russian threat perceptions and contributed to strategic friction: some U.S. policy documents and commentators now signal a pause or end to expansion as a major policy shift with big implications for Ukraine’s ambitions [5] [6].
2. Moscow’s narrative and Western counter‑narratives
The Kremlin portrays NATO enlargement as a primary cause of its insecurity and uses that framing to justify its policy choices; this Russian framing is reiterated in official commentary about recent U.S. strategy shifts [7]. Western scholarship and institutions, including historians and analysts cited in reporting, stress that NATO enlargement also followed desires of new democracies to anchor themselves in Euro‑Atlantic security and that the alliance’s “open door” was meant to extend stability rather than provoke [1] [8].
3. NATO expansion and the Ukrainian question
Ukraine’s application for NATO membership in 2022 and subsequent diplomatic friction made Kyiv’s aspirations a flashpoint. Recent U.S. national security guidance and some reporting indicate a U.S. policy turn that would end the expectation of perpetual NATO enlargement and thus foreclose Ukrainian membership in the near term—an outcome that would reshape the logic of deterrence in Europe and could amount to granting Russia an effective veto over enlargement in practice [5] [6] [9].
4. EU integration: civilian power meets defence cooperation
Since 2014 the EU has deepened security and defence measures—publishing instruments such as the Strategic Compass and boosting integrated exercises—and has coordinated more closely with NATO on crisis management and defence industry planning, reinforcing Europe’s collective readiness [3] [4]. The EU’s push for “strategic autonomy” and for more European defence spending is presented as complementary to NATO’s work, not a replacement; NATO and EU bodies have formal mechanisms (PACE, joint exercises) to synchronize planning [4] [2].
5. Transatlantic strains and the shifting U.S. posture
Analysts at CSIS and reporting from Kyiv and elsewhere describe U.S. policy in 2025 as a significant inflection point: new U.S. guidance reportedly downgrades Europe as a priority and signals an end to NATO enlargement—moves that prompt debate about whether Europe must assume greater defence burdens or face a partial U.S. withdrawal from coordination mechanisms [5] [6] [10]. These tensions expose competing agendas: Washington balancing global priorities, European governments seeking autonomy, and critics warning about hollowing out collective deterrence [6] [11].
6. Scenarios: what ending expansion or excluding Ukraine would mean
If NATO enlargement is explicitly curtailed, commentators argue it could freeze the alliance’s post‑Cold War trajectory and leave Ukraine dependent on informal guarantees or a “frozen” security arrangement; one policy analysis frames such a deal as stopping the fighting but inflicting “a deep wound on the transatlantic alliance” by effectively conceding Russian influence over enlargement [9]. Alternative views in NATO and EU documents stress deeper cooperation and burden‑sharing as a way to preserve deterrence even without further immediate expansion [4] [11].
7. Limitations, competing claims and what sources do not say
Available sources document the political debate and policy documents about enlargement and EU–NATO cooperation but do not provide a definitive causal accounting that proves enlargement alone caused the conflict; historians and analysts offer competing interpretations—some emphasize Russian revanchism, others the cumulative effects of eastward NATO growth [8] [1]. Sources also reflect differing political agendas: Kremlin and sympathetic outlets highlight U.S./NATO culpability [7] [12], while Western institutions emphasize state choice and collective defence [1] [2].
8. Bottom line: two forces, one contested explanation
NATO enlargement and EU integration are both instruments that reshaped post‑Cold War security and contributed to Ukraine’s Western orientation; they strengthened Kyiv’s options while also becoming focal points in Russian grievances and in debates over alliance limits. Whether these policies “caused” the conflict is disputed across sources; the immediate policy consequence now is a re‑examination of enlargement, growing EU–NATO cooperation on readiness, and a volatile transatlantic debate over how to preserve deterrence if formal enlargement is paused [1] [4] [5].