John Mearsheimer, one of the most distinguished academics in the discipline of International Relations, has sparkled a large academic and public debate on the causes of the crisis in Ukraine. He has repeatedly argued that the West is principally responsible as NATO’s expansion posed a vital threat to Russia’s security and therefore motivated Putin’s 2014 annexation of Crimea and the 2022 invasion of Ukraine. This article rebuffs his interpretation as one-sided. The analysis of facts and diplomatic documents about the 2008 Bucharest NATO Summit, the NATO enhanced opportunity partnership and the supposed promises that the West made to Russia after the Cold War show a more nuanced story. Historical events are the result of the complex interplay of several factors and actors. Western mistakes have to be acknowledged, yet the Kremlin’s revisionism and its fear of the expansion of Western values are the root causes of the situation in Ukraine.