Is NATO Expansion the True Cause of the Ukraine War?

Declassified U.S. documents and statements by key diplomats, including U.S. Secretary of State James Baker and Soviet leader Mikhail Gorbachev, confirm that Western leaders gave verbal assurances in 1990 that NATO would not expand 'one inch eastward' beyond a reunified Germany. The 1997 NATO-Russia ounding Act, which established a partnership, did not legally forbid enlargement, but Russian officials and many scholars argue that the subsequent waves of expansion (1999, 2004, 2009) violated the spirit of these assurances, directly fueling Russian security fears that culminated in the 2022 invasion of Ukraine.

In a widely cited 2022 analysis, University of Chicago political scientist John Mearsheimer argues that NATO's eastward expansion, particularly the alliance's 2008 Bucharest declaration that Ukraine and Georgia 'will become members,' was the root cause of the war. He points to NATO missile defense systems in Romania and Poland, deployed since 2016, as capable of undermining Russia's nuclear deterrent, and notes that by 2021, NATO had conducted over 40 exercises near Russia's borders. Mearsheimer concludes that Moscow's invasion was a strategic, defensive reaction to an existential threat, not an unprovoked imperial adventure.

A comprehensive report by the International Criminal Court (ICC) and corroborating evidence from the U.N. High Commissioner for Human Rights documents that Russia's invasion was planned months in advance, with troop buildups along Ukraine's borders beginning in late 2021, before any new NATO membership offer. The report highlights that Russia invaded Georgia in 2008 and annexed Crimea in 2014, when NATO membership for these states was not a near-term possibility. Analyst Michael Kofman of CNA argues that Putin's speeches, including his 2021 essay 'On the Historical Unity of Russians and Ukrainians,' reveal a revisionist ideology aimed at erasing Ukrainian statehood, not a defensive posture against Western missiles.

Data from the Kyiv International Institute of Sociology shows that Ukrainian public support for NATO membership was below 30% before 2014, but surged to over 60% after Russia's annexation of Crimea and the start of the Donbas war. This timeline contradicts the claim that NATO expansion provoked Russia; rather, it was Russia's aggression that drove Ukraine toward the alliance. Additionally, the 1994 Budapest Memorandum, under which Ukraine gave up its nuclear arsenal in exchange for security assurances from Russia, was violated by Russia's 2014 annexation, demonstrating that even a neutral, non-NATO Ukraine was not safe from Russian revanchism.