“Although the British wisely left their colony peacefully in 1947, the violence that accompanied partition sapped the development of the two states and set the stage for three wars between them.” —Selig S. Harrison, Paul H. Kreisberg, and Dennis Kux

India and Pakistan together account for one fifth of the world’s population. Their size and influence have made the continued conflict between them a long-standing cause of global concern. Their adversarial relationship has been marked by three major wars, rival allegiances with other powers (including China, the former Soviet Union, and the United States), many military skirmishes and violent incidents, and a nuclear arms buildup. Both nations trade accusations of meddling in each other’s internal affairs and of fomenting violence and civil unrest.

To understand the persistent hostility between these two nations, it is necessary to go back to the circumstances of...