On August 9, 1945 a B-29 Superfortress named Bockscar dropped an atomic bomb codenamed "Fat Man" on the city of Nagasaki. Three days earlier, on August 6, the atomic bomb codenamed "Little Boy" was dropped on the city of Hiroshima. It is estimated that 60,000 to 80,000 people died in Nagazaki from the atomic bomb, while 90,000 to 160,000 died in Hiroshima. Several of those who died were unintended victims, including U.S. POW's and foreign students studying in Japan.
These events ushered in a new era of warfare that changed the geopolitical landscape of the 20th and 21st century. You can learn more about these events by either reading documents available at the Harry S. Truman library, browsing Milwaukee Public Library's collection of books on the topic, or watching the award winning White Light/Black Rain.