At 8:15am on August 6, 1945, the United States of America dropped an atomic bomb on the city of Hiroshima, in western Japan, instantly killing tens of thousands of children, women, and men living there, and leaving tens of thousands more maimed and poisoned by radiation.
The Wikipedia has an extensive Atomic bombings of Hiroshima and Nagasaki article. If you take time to read it, you might also want to read the Bombing of Tokyo in World War II article, which details the bombing campaign against Tokyo during the war (part of a campaign that resulted in the some 500,000 people being killed throughout Japan, and another 8 million being left homeless).
The article includes some details about the so-called “Great Tokyo Air Raid”: the March 10, 1945 firebombing of Tokyo, which killed more than 100,000 people in a single night.
The U.S. Strategic Bombing Survey would later write that during the March 10 firebombing of Tokyo “probably more persons lost their lives by fire at [sic] Tokyo in a six-hour period than at any time in the history of man.”
Last March, Masaru Fujimoto wrote a couple of related articles for the Japan Times: ‘Scorched and boiled and baked to death’ about the Great Tokyo Air Raid, and ‘The executioner of Tokyo’, about Gen. Curtis E. LeMay, the man who commanded the bombing campaigns.