The atomic bombings of Hiroshima and Nagasaki were nuclear attacks ordered by President Truman against the Empire of Japan. The attacks were carried out on August 6 and 9, 1945, respectively, which contributed, together with the Soviet-Japanese War, to the surrender of Japan and the end of the Second World War.
With the Manhattan project, nuclear weapons continued to be built. Although it was very secret, the information leaked to the Soviet Union, with which the US lost its nuclear hegemony.
In this way, both countries agreed on the non-use of nuclear weapons in war conflicts (Nuclear Non-Proliferation Treaty), since they knew that a large-scale nuclear war would put at risk the very existence of a large part of the world's population.