Will a strategy change toward one of “hearts and minds” alter the eventual outcome of the American-led allied war effort in Afghanistan? We investigate this question by analyzing 66 cases of counterinsurgency warfare from the twentieth century in which a foreign power seeks to defend a central authority in a state or colonial territory against an insurgency. We identify whether and when a foreign power implemented a change in its counterinsurgency strategy, whether said change involved a shift toward a strategy reflecting a hearts and minds emphasis, as well as the foreign power's eventual success or failure in prevailing over insurgents. We find that while shifting toward a strategy of hearts and minds increases the chances for success, the improvement is modest and requires nearly a decade to produce. Furthermore, we find that the impact of a strategy change is conditional on the timing of the change, with a “window of opportunity” associated with success closing after approximately eight years of war. Our findings bode poorly for allied efforts in contemporary Afghanistan.