The world's first nuclear explosion occurred on July 16, 1945, during the Trinity test. (Department of Energy)
An atomic bomb is a weapon of mass destruction deriving its energy from nuclear fission. The first atomic bomb was exploded at Alamogordo, New Mexico, on 16 July 1945. The code name for the test was "Trinity." As in the case of the bomb dropped over Hiroshima, Japan, a few weeks later (August 6), the fissionable material was uranium-235. However, when Nagasaki was destroyed by another bomb three days after that plutonium-239 was used. Together the Hiroshima and Nagasaki bombs killed more than 100,000 people. Since the early 1950s, the power of the fission bomb (equivalent to some 20,000 tons of TNT in the case of the Hiroshima bomb) has been vastly exceeded by that of the hydrogen bomb which depends on nuclear fusion.
Today, the official nuclear powers are:
Additionally, North Korea detonated a few small nuclear explosions in 2006.
The dates refer to the first nuclear detonations.