Is NATO Expansion the Real Cause of the Ukraine War?

This article examines the historical record of verbal assurances given to Soviet leader Mikhail Gorbachev in 1990 regarding NATO's eastward expansion. It highlights that while U.S. Secretary of State James Baker offered informal assurances that NATO would not move 'one inch eastward,' no formal treaty or binding agreement was signed. The piece argues that the ambiguity of these verbal commitments fueled Russian grievances, but ultimately, NATO's enlargement was a sovereign decision of independent states, not a violation of a legal pledge.

This Reuters analysis details the timeline of Ukraine's aspirations to join NATO, from the 2008 Bucharest summit declaration to the 2014 Revolution of Dignity and the 2022 invasion. It cites Western officials arguing that NATO's open-door policy is a defensive measure, allowing sovereign nations to choose their security alliances. The article emphasizes that Russia's 2014 annexation of Crimea and support for separatists in Donbas occurred before any concrete NATO membership offer to Ukraine, undermining the claim that expansion triggered the war.

This academic paper by John J. Mearsheimer, a leading realist scholar, argues that NATO's eastward expansion, particularly the prospect of Ukraine joining, was the primary cause of the Ukraine war. Mearsheimer contends that the West's actions encroached on Russia's core strategic interests, leaving Moscow with little choice but to respond militarily. He cites the 1990 assurances, the 1999 bombing of Yugoslavia, and the deployment of missile defense systems as evidence of NATO's offensive posture. The paper concludes that the war is a tragic consequence of Western provocation, not unprovoked aggression.

This report from the Brookings Institution analyzes the 1994 Budapest Memorandum, in which Ukraine gave up its nuclear arsenal in exchange for security assurances from Russia, the U.S., and the UK. The paper argues that Russia's 2014 annexation of Crimea and the 2022 invasion violated these guarantees, demonstrating that Moscow's aggression predates any NATO expansion push. It highlights that Ukraine's desire for NATO membership grew out of a need for real security after Russia broke its promises, framing NATO enlargement as a response to Russian aggression, not a cause.