(International Politics) Abstract: It is often claimed that NATO’s post-Cold War geographic enlargement threatened Russian security interests and caused the downturn in Russia’s relations with the West. This article unpacks and challenges that causal claim, making three basic arguments. First, NATO enlargement made the alliance weaker. Russia knew this and did not react militarily to any perceived threat from Europe until after it seized Crimea in 2014. Second, the downturn in Russia’s relationship with the West was overdetermined and most likely caused by Russia’s reaction to its own declining influence in the world. While NATO’s geographic enlargement aggravated this situation, it was probably not the most significant causal factor. Third, while Russia certainly reacted negatively to NATO enlargement right from the start, the reaction was manipulated and magnified by both the nationalist opposition, and Vladimir Putin’s regime, to serve domestic political interests.