Is NATO Expansion the Root Cause of War?

Declassified documents and memoirs confirm that in 1990, U.S. Secretary of State James Baker assured Soviet leader Gorbachev that NATO would not move 'one inch eastward' in exchange for German reunification. Despite this, NATO admitted Poland, Hungary, and the Czech Republic in 1999. In a 1997 New York Times op-ed, George Kennan, the architect of containment, called this expansion 'the most fatal error of American policy,' predicting it would inflame Russian nationalism and lead to a new Cold War. These expert warnings and broken assurances provide strong evidence that NATO expansion was a provocative act, not a defensive one, and contributed to the security dilemma that preceded the 2022 invasion of Ukraine.

A comprehensive analysis by the Wilson Center documents a consistent pattern of Russian/Soviet military interventions to suppress sovereignty in neighboring states, including the invasions of Hungary (1956), Czechoslovakia (1968), Georgia (2008), and Ukraine (2014 and 2022). The report argues that Russia's invasion of Ukraine is not a reaction to NATO's post-Cold War expansion but a continuation of a centuries-old imperialist drive to dominate its 'near abroad.' It notes that Russia invaded Georgia in 2008 while NATO expansion had stalled, and invaded Ukraine in 2014 despite no immediate NATO membership offer, undermining the claim that NATO growth was the root cause.

This article from the Brookings Institution highlights that NATO is a defensive alliance under Article 5 of the Washington Treaty, which commits members to collective defense, not offense. It emphasizes that every post-Cold War enlargement (1999, 2004, 2009, 2017, 2020, 2024) was the result of sovereign nations voluntarily applying for membership to escape Russian influence, not coercion by the U.S. The piece cites that NATO's 1999 bombing of Serbia was a humanitarian intervention to stop ethnic cleansing in Kosovo, authorized by UN Security Council resolutions, and that NATO has never initiated a territorial conquest. It concludes that blaming NATO expansion for Putin's invasion excuses the aggressor and ignores Moscow's own actions.

A detailed report from the Quincy Institute for Responsible Statecraft documents NATO's 2011 intervention in Libya, which went beyond a UN-authorized no-fly zone to actively support rebel forces in overthrowing Muammar Gaddafi. The intervention destroyed a functioning state, leading to a decade of civil war, weapons proliferation, and a refugee crisis. The report argues that this action, along with the 1999 bombing of Serbia (which was conducted without UN Security Council approval), demonstrates that NATO is not purely defensive but has engaged in regime change, creating a pattern of aggression that Russia views as an existential threat. This evidence supports the con argument that NATO's actions, not just its expansion, have fueled geopolitical instability.