That bomb — and a second atomic blast on Nagasaki on Aug. 9 — effectively ended World War II; Japan surrendered six days after the Hiroshima bombing. However, the human costs were huge. Estimates of those killed go as high as 150,000, and even for those who survived, it was a hellish, life-altering experience. At the same time, many believe that the bomb was preferable to a planned invasion of Japan, which would have likely brought massive casualties among civilians, Japanese forces and Allies.
During his visit to the city, Obama is expected to give a speech on nonproliferation of nuclear weapons — a topic that he has touched on many times before. He is not expected to apologize for the bombing itself.