From the Wikipedia entry for Hiroshima:
On August 6, 1945 the nuclear weapon Little Boy was dropped on Hiroshima by Enola Gay, a U.S. Air Force B-29 bomber which was altered specifically to hold the bomb, killing an estimated 200,000 people and heavily damaging 80% of the city.[citation needed] In the following months, an estimated 60,000 more people died from injuries or radiation poisoning.[citation needed] Since 1945, several thousand more hibakusha have died of illnesses caused by the bomb. It was the second such device to be detonated (the first being the successful test at the Manhattan Project's desert test site, in New Mexico), and the first ever to be used in military action. The American atomic bombings of Hiroshima and Nagasaki were major factors that led to the Japanese surrender, and the official end of World War II.
And a few words more
I still have a newspaper with the A-Bomb headline. At the time, my father, 3 maternal uncles & 7 great uncles were in various places of the Pacific & Europe. My mother's brother was killed at Aachen, Germany. My father was on a troop ship that the Japanese torpedoed & sank--he survived in a liferaft.
All of my family, to this day, believes that using the atomic bombs was justified. They were convinced that destroying Hiroshima & Nagasaki ended the war early & saved the lives of tens of thousands of US military personnel--including some of them, personally.
There are revisionist opinions & there are some who think or believe or feel that the annihilation of so many civilians was too much. Some people also think that the targeting of civilian populations altered how any nation can take the so-called "high moral ground" in modern warfare. And there are some people who consider the use of nuclear weapons inherently wrong.
The horror of these bombings & the aftermath defy any type of analysis. Even today, the images are repellant. And it is a part of our history as US citizens.