The bright flash that lit up the sky over Hiroshima on the morning of<br > August 6， 1945 signaled both the end of World War 1I and the dawn of the<br > nuclear age. A week later， Japan surrendered and the world was at peace<br > after six years of righting in Europe and eight in Asia. Yet Americans were<br >never able to enjoy the peace they had looked forward to so fervently; the<br >rapid onset of the Cold War with the Soviet Union kept international tensions<br >at a dangerously high level and prevented any return to normalcy. Soon both<br >superpowers possessed nuclear weapons and became locked in an escalating<br >arms race that cast a long shadow over every aspect of postwar American life.<br > The man who made the decision to drop the atomic bomb had been in of-<br >rice only three months. Harry S. Truman became President on April 12， 1945<br >with the sudden death of Franklin D. Roosevelt， and he took up his duties<br >with a staggering number of handicaps. Despite his declining health， FDR had<br >failed to prepare his successor， keeping Truman in ignorance about vital mili-<br >tary and diplomatic policies and refusing even to inform him of the atomic<br >bomb project. In contrast to Roosevelt， Truman was a relatively obscure<br >senator from Missouri who had built a modest reputation through his Congres-<br >sional investigations of defense and war industries; he had won the respect of<br >his fellow senators， but had made only a slight impact on the public at large.<br >Powerful groups within the Democratic party， particularly southern leaders<br >and big city bosses， had forced Roosevelt to dump Henry Wallace， his wartime<br >Vice-President who leaned to the left， and Truman had emerged with the nom-<br >