HIROSHIMA AND NAGASAKI

In August 1945, during the final stage of the Second World War, the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki. The two bombings, which killed at least 129,000 people, remain the only use of nuclear weapons for warfare in human history.
As the Second World War entered its sixth and final year, the Allies had begun to prepare for, what was anticipated to be, a very costly invasion of the Japanese mainland. This was preceded by an immensely destructive firebombing campaign that obliterated many Japanese cities. The war in Europe had concluded when Nazi Germany signed its instrument of surrender on May 8, 1945, but with the Japanese refusal to accept the Allies' demands for unconditional surrender, the Pacific War dragged on. Together with the United Kingdom and China, the United States' calls for the unconditional surrender of the Japanese armed forces in the Potsdam Declaration on July 26, 1945 was buttressed with the threat of "prompt and utter destruction".
 The Manhattan Project
Even before the outbreak of war in 1939, a group of American scientists–many of them refugees from fascist regimes in Europe–became concerned with nuclear weapons research being conducted in Nazi Germany. In 1940, the U.S. government began funding its own atomic weapons development program, which came under the joint responsibility of the Office of Scientific Research and Development and the War Department after the U.S. entry into World War II. The U.S. Army Corps of Engineers was tasked with spearheading the construction of the vast facilities necessary for the top-secret program, codenamed “The Manhattan Project ” (for the engineering corps’ Manhattan district).

 Did you know??
 After World War II, most of Hiroshima would be rebuilt, though one destroyed section was set aside as a reminder of the effects of the atomic bomb. Each August 6, thousands of people gather at Peace Memorial Park to join in interfaith religious services commemorating the anniversary of the bombing.

 Over the next several years, the program’s scientists worked on producing the key materials for nuclear fission–uranium-235 and plutonium (Pu-239). They sent them to Los Alamos, New Mexico, where a team led by J. Robert Oppenheimer worked to turn these materials into a workable atomic bomb. Early on the morning of July 16, 1945, the Manhattan Project held its first successful test of an atomic device–a plutonium bomb–at the Trinity test site at Alamogordo, New Mexico.