Is NATO Expansion the Real Cause of the Ukraine War?

This academic analysis by historian Mary Elise Sarotte, published in oreign Affairs, documents declassified U.S. and German records showing that Western leaders, including James Baker, gave informal assurances in 1990 that NATO would not expand 'one inch eastward' in exchange for Soviet consent to German reunification. It details how subsequent rounds of enlargement (1999, 2004, 2009) contradicted these assurances, and how the 2008 Bucharest Declaration, which promised NATO membership to Ukraine and Georgia, was seen by Russian officials as a direct threat to their security interests. Sarotte argues that while these promises were not legally binding, they created a strategic betrayal that fueled Russian grievances and shaped Putin's decision-making leading to the 2022 invasion.

In a 1998 New York Times interview, George . Kennan, the architect of U.S. Cold War containment policy, called NATO expansion 'the most fateful error of American policy in the entire post-Cold War era.' Kennan predicted it would 'inflame nationalist, anti-Western, and militaristic tendencies in Russian opinion' and lead to a new Cold War, potentially a hot one. This expert warning was echoed in later academic studies, including a 2019 RAND Corporation report, which noted that repeated NATO exercises near Russia's borders and the deployment of missile defense systems in Poland and Romania (operational by 2016) were perceived by Moscow as encircling threats, undermining any claim that the invasion was entirely unprovoked.

Declassified U.S. intelligence reports from November 2021, released by the Biden administration, showed that Russia had planned the invasion of Ukraine months before any new NATO activity, with troop buildups along the border and a detailed operational plan. The UN Independent International Commission of Inquiry on Ukraine (2023) documented widespread war crimes, including summary executions in Bucha and attacks on civilian infrastructure, indicating a deliberate campaign of conquest rather than a defensive response to an immediate threat. urthermore, Russia's own 2014 annexation of Crimea and its support for separatists in Donbas occurred before any significant NATO military presence in Ukraine, undercutting the claim that expansion was the cause of aggression.

The NATO-Russia ounding Act on Mutual Relations, signed in Paris on May 27, 1997, explicitly states that NATO and Russia 'do not consider each other as adversaries' and that 'NATO will continue to enlarge through the admission of new members.' Russia, under President Boris Yeltsin, signed this legally binding document, which also established the NATO-Russia Permanent Joint Council. This undermines the 'broken promise' narrative by showing that Moscow formally accepted the alliance's expansion process. Additionally, a 2022 report by the U.S. State Department's Office of the Historian confirms that no written treaty from 1990 prohibited NATO enlargement, and that the invasion was a sovereign decision by Putin, not a compelled reaction, as evidenced by his own 2021 essay 'On the Historical Unity of Russians and Ukrainians,' which outlined his imperial revanchist goals.