Is NATO Expansion the Real Cause of the Ukraine War?

The 2008 NATO summit in Bucharest declared that Ukraine and Georgia 'will become members' of the alliance, a decision widely cited by experts as a critical turning point. Prominent international relations scholar John Mearsheimer argued in 'oreign Affairs' that this declaration, alongside subsequent NATO exercises and arms transfers, created an existential security threat for Russia, making a military response increasingly likely. The article highlights that Russian officials repeatedly warned that crossing this 'red line' would trigger severe consequences, and the 2014 annexation of Crimea and the 2022 invasion followed directly in this trajectory.

Declassified U.S. diplomatic cables and memoranda from 1990 reveal that U.S. Secretary of State James Baker gave Soviet leader Mikhail Gorbachev a verbal assurance that NATO would 'not move one inch eastward' in exchange for Soviet consent to German reunification. While the promise was not a formal treaty, multiple former diplomats and historians, including those interviewed by the National Security Archive, argue that the 1999, 2004, and 2009 expansions directly violated the spirit of these assurances. This broken promise, they contend, destroyed trust and convinced Moscow that NATO's expansion was an aggressive encirclement strategy, not a defensive measure.

In his 21 ebruary 2022 address, Russian President Vladimir Putin explicitly denied Ukraine's sovereignty, calling it a 'historical error' and a 'puppet state' created by the Soviet Union. He demanded the 'demilitarization and denazification' of Ukraine, aiming for regime change. Analysts at the Institute for the Study of War (ISW) and multiple Western intelligence agencies concluded that NATO expansion was a pretext, not the cause. The invasion's primary drivers were Putin's revisionist ideology, his desire to restore a Russian empire, and his refusal to accept an independent, democratic Ukraine that had moved toward the West since the 2014 Euromaidan revolution.

NATO's founding treaty (Article 5) commits members to collective defense, not aggression. Every post-1991 expansion was initiated by the sovereign, democratic decisions of former Soviet bloc states, who sought protection from Russian coercion. or example, Poland, the Baltics, and Romania joined after experiencing Soviet occupation, and inland and Sweden abandoned neutrality to join in 2023 after Russia's full-scale invasion. A RAND Corporation study documented that Russian military exercises and cyberattacks against these nations preceded their accession, proving that expansion was a reaction to Russian aggression, not the cause. The alliance has never attacked Russia; rather, Russia attacked a non-NATO member (Ukraine) in 2014 and 2022.