Many thousands took advantage of a brief lull in the fighting to flee the Swat district of Pakistan, where government troops are engaged in a major offensive against forces of the Taliban. Escape was possible for only a few hours before the army reimposed the curfew. But if the exodus from the Swat Valley continues at its current rate, the region could be contemplating the biggest displacement of people since the partition of British India in 1947.

This vast movement of people, and the toll of human misery it represents, is the most immediate cost of the Pakistan government's latest effort to stall the Taliban's advance. Three months ago, Islamabad concluded a truce with rulers in the Swat district that included the recognition of sharia law there in the hope that peace,...