The massive US atomic initiative, the Manhattan Project, developed as a response to German scientists creating a nuclear weapon in the 1930s. Before World War II has stricken the international community, a threat of nuclear conflict was already there. Besides Germany, the Soviet Union also evoke major concerns in the US officials. That is why developing a strong nuclear weapon seemed to guarantee safety to America.
In 1939, President Roosevelt declared the agencies that would work on the Manhattan Project. Testing of nuclear reactions was conducted in the remote areas of New Mexico, Tennessee, and Washington. In 1941, Japan attacked Pearl Harbor, Hawaii, and the president declared war immediately. At this time, scientists actively worked on developing nuclear weapons. In 1943, bombs were already built and tested at Los Alamos Laboratory, New Mexico. The Manhattan Project finished with the US nuclear attack on Japanese cities of Hiroshima and Nagasaki. These events pushed Japan to surrender.