Economics
The Prisoner's Dilemma in Interstate Cooperation
Quick fact
In the classic prisoner's dilemma, two rational players both choose to defect even though cooperating would make both better off—a result so common that it helps explain why nations often fail to cooperate on issues like arms control or environmental protection.
Why this is interesting
You and a friend both want the last slice of cake. If you both take half, you're both happy. But if you grab the whole thing, you get more—until your friend does the same next time. In international politics, this same puzzle plays out with nuclear weapons, trade, and climate change.