Throughout July 1945 the Japanese mainlands, from the latitude of Tokyo on Honshu northward to the coast of Hokkaido, were bombed just as if an invasion was about to be launched. In fact, something far more sinister was in hand, as the Americans were telling Stalin at Potsdam.

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In 1939 physicists in the United States had learned of experiments in Germany demonstrating the possibility of nuclear fission and had understood that the potential energy might be released in an explosive weapon of unprecedented power. On August 2, 1939, Albert Einstein had warned Roosevelt of the danger of Nazi Germany’s forestalling other states in the development of an atomic bomb. Eventually, the U.S. Office of Scientific Research and Development was created in June 1941 and given joint responsibility with the war department in the Manhattan Project to develop an atomic bomb. After four years of intensive and ever-mounting research and development efforts, an atomic device was set off on July 16, 1945, in a desert area near Alamogordo, New Mexico, generating an explosive power equivalent to that of more than 15,000 tons of TNT. Thus the atomic bomb was born. Truman, the new U.S. president, calculated that this monstrous weapon might be used to defeat Japan in a way less costly of U.S. lives than a conventional invasion of the Japanese homeland. Japan’s unsatisfactory response to the Allies’ Potsdam Declaration decided the matter. (See Sidebar: The decision to use the atomic bomb.) On August 6, 1945, an atomic bomb carried from Tinian Island in the Marianas in a specially equipped B-29 was dropped on Hiroshima, at the southern end of Honshu: the combined heat and blast pulverized everything in the explosion’s immediate vicinity, generated fires that burned almost 4.4 square miles completely out, and immediately killed some 70,000 people (the death toll passed 100,000 by the end of the year). A second bomb, dropped on Nagasaki on August 9, killed between 35,000 and 40,000 people, injured a like number, and devastated 1.8 square miles.

The Japanese surrender

News of Hiroshima’s destruction was only slowly understood in Tokyo. Many members of the Japanese government did not appreciate the power of the new Allied weapon until after the Nagasaki attack. Meanwhile, on August 8, the U.S.S.R. had declared war against Japan. The combination of these developments tipped the scales within the government in favour of a group that had, since the spring, been advocating a negotiated peace. On August 10 the Japanese government issued a statement agreeing to accept the surrender terms of the Potsdam Declaration on the understanding that the emperor’s position as a sovereign ruler would not be prejudiced. In their reply the Allies granted Japan’s request that the emperor’s sovereign status be maintained, subject only to their supreme commander’s directives. Japan accepted this proviso on August 14, and the emperor Hirohito urged his people to accept the decision to surrender. It was a bitter pill to swallow, though, and every effort was made to persuade the Japanese to accept the defeat that they had come to regard as unthinkable. Even princes of the Japanese Imperial house were dispatched to deliver the Emperor’s message in person to distant Japanese Army forces in China and in Korea, hoping thus to mitigate the shock. A clique of diehards nevertheless attempted to assassinate the new prime minister, Admiral Suzuki Kantarō; but by September 2, when the formal surrender ceremonies took place, the way had been smoothed.

Truman designated MacArthur as the Allied powers’ supreme commander to accept Japan’s formal surrender, which was solemnized aboard the U.S. flagship Missouri in Tokyo Bay: the Japanese foreign minister, Shigemitsu Mamoru, signed the document first, on behalf of the Emperor and his government. He was followed by General Umezu Yoshijiro on behalf of the Imperial General Headquarters. The document was then signed by MacArthur, Nimitz, and representatives of the other Allied powers. Japan concluded a separate surrender ceremony with China in Nanking on September 9, 1945. With this last formal surrender, World War II came to an end.