A distinguished historian of transatlantic relations revisits Western relations with Russia during the 1990s. This critical decade set the tone for geopolitics in the post–Cold War period, above all though the expansion of NATO. Sarotte weaves together the most engaging and carefully documented account of this period in East-West diplomacy currently available. She deepens the conventional wisdom among most historians, namely that in the late 1980s and early 1990s, many Western leaders gave informal assurances that NATO would not expand—not just to the territory of the former East Germany but also across central and eastern Europe. Since Moscow failed to secure any formal guarantee, however, Western leaders later went ahead anyway, downplaying or denying any contradiction. She argues more speculatively that this perceived betrayal was a major factor in the subsequent collapse of democracy in Russia and the further deterioration of relations between the West and Russia under President Vladimir Putin. But most of the book’s evidence actually leans in the opposite direction and suggests that U.S. Presidents George H. W. Bush and Bill Clinton and their top diplomats slowed NATO expansion to try to stabilize the government of Russian President Boris Yeltsin in the short term and held off as long as he still looked viable. It was only when Yeltsin’s fall became imminent, and a hardening of East-West relations started to seem inevitable, that the United States moved to expand the alliance.