How do temporal calculations—whether to address a challenge in the near term or defer resolution to the future—affect international politics? For a matter at the heart of a number of problems in international relations, this question has received little systematic treatment. Several studies address individual leaders’ time horizons; others assess how different domestic institutions incentivize long-term or short-term thinking. Still, aside from classic work in regime theory highlighting the importance of extending the “shadow of the future” for international cooperation, the impact of states’ time horizons on world politics remains understudied.

Enter David Edelstein in his insightful Over the Horizon: Time, Uncertainty, and the Rise of Great Powers. For Edelstein, states face what he calls “now or later” dilemmas. Like Hamlet debating whether to seek Denmark's throne, states facing an international problem can choose to incur short-term costs to address a potential long-term problem or punt now but potentially pay larger costs to resolve the matter in the future. States with longer time horizons prefer the former: seeking to minimize costs, they prefer to act now to create a better long-term future. Conversely, states with shorter time horizons—looking to keep immediate costs low—defer re