Around the world, there are millions of hostile rivalries, yet only a fraction erupt into violence, a fact too many accounts overlook. With a counterintuitive approach, Christopher Blattman reminds us that most rivals loathe one another in peace. War is too costly to fight, so enemies almost always find it better to split the pie than spoil it for everyone or struggle over thin slices. In those rare instances when fighting ensues, we should ask: What kept rivals from compromise? Why We Fight draws on decades of economics, political science, psychology, and real-world interventions to lay out the root causes and remedies for war, showing that violence is not the norm; that there are only five reasons why conflict wins over compromise; and how peacemakers turn the tides through tinkering, not transformation. From warring states to street gangs, ethnic groups and religious sects to political factions, there are common dynamics to heed and lessons to learn. Realistic and optimistic, this is a book that lends new meaning to the adage "Give peace a chance."