One bombing, two verdicts
In August 1945 the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki, and Japan surrendered. Both sides of the argument that followed accept that sequence of events. They split over why it happened and what it led to.
Supporters of the decision say the bombs ended the war quickly and spared the American and Allied soldiers who would have died in a longer fight. Critics read the same events another way. They argue that Washington knew Japan was already close to surrender, so the bombs were unnecessary for victory. On their reading the real audience was Moscow. The bombs showed the Soviet Union how powerful the United States had become and helped hold back Soviet gains in Asia and beyond.
In 1965 the historian Gar Alperovitz took the critics' case further in Atomic Diplomacy: Hiroshima and Potsdam. He blamed President Truman's decision for, in effect, starting the Cold War. One event can therefore close a war in one account and open a new one in another.
Neither side disputes that the bombs fell or that Japan surrendered. The disagreement is about motive and significance, which is where most arguments between historians take place.
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