From Ohio History Central
The Manhattan Project was the code name given to the efforts of the United States, Great Britain and Canada to develop the first atomic bomb during World War II.
Numerous countries involved in World War II sought to develop a nuclear weapon. Scientists in Great Britain, Canada, and the United States worked to create a bomb capable of ending the war swiftly. These scientists focused on nuclear fission as the means to make such a bomb. At the same time, German scientists were also working to develop such a weapon.
In the United States, physicist J. Robert Oppenheimer and General Leslie R. Groves spearheaded the drive to create this weapon. Groves formally named the attempt the "Manhattan Engineering District," since his headquarters was located in Manhattan, New York, although the effort became better known as the "Manhattan Project." Oppenheimer and Groves concentrated research efforts in Hanford, Washington, Los Alamos, New Mexico, and Oak Ridge, Tennessee, although numerous other centers, including the Battelle Institute in Columbus, Ohio, participated in the development of the bomb. Eventually 130,000 people participated in the Manhattan Project.
By July 1945, scientists had developed three atomic bombs. After a successful test of the first bomb near Alamogordo, New Mexico, on July 16, 1945, President Harry Truman authorized the United States military to utilize another atomic bomb against Japan, one of the United States' enemies in World War II. On August 6, 1945, the crew of the Enola Gay dropped an atomic bomb on Hiroshima, Japan. Approximately 200,000 people died. This atomic bomb, nicknamed Little Boy, along with a second atomic bomb, dropped on Nagasaki, Japan on August 9, 1945, prompted the Japanese government to surrender. World War II was now over.
The atomic bomb did help the United States attain victory over Japan during World War II. Unfortunately, the atomic bomb's development prompted other nations to develop similar weapons. While the United States had a monopoly on the atomic bomb between 1945 and 1949, the Soviet Union developed its own weapon of mass destruction in 1949, helping to divide the world even further during the Cold War.