The American use of atomic bombs against the Japanese cities of Hiroshima on August 6, 1945, and Nagasaki on August 9, 1945 — killing approximately 200,000 people immediately and tens of thousands more from radiation — which ended the Second World War in the Pacific and inaugurated the nuclear age: a permanent condition of human civilization in which the means to destroy it exist and cannot be uninvented.
Before August 6, 1945, every weapon in human history had been limited. A city could be burned, an army destroyed, a population besieged — but the destruction required effort proportional to its scale. One plane, one bomb, one city: Hiroshima changed that ratio permanently. The knowledge that produced Little Boy cannot be forgotten. The world that existed before August 6 — in which war was terrible but its scale was bounded by human capacity — ended that morning and has not returned.