The first atomic bomb was detonated on this day in 1945 [Trinity]. The second detonation of an atomic bomb took place over Hiroshima, Japan, on August 6, 1945.
So far, Hiroshima and Nagasaki are the only examples of a nuclear device being used in war. We've managed to avoid dropping atomic bombs on each other for 67 years. If you think about it, that's a pretty remarkable achievement.