why did the u.s drop the bomb hiroshima
1 The US dropped the Atom Bomb on Hiroshima after the sneak attack on Pearl Harbor during WWII. 2  It was the first Atom Bomb to ever be used, and was not the last. 3  The second Atom Bomb was dropped on Nagasaki which was the final straw in ending WWII this day is called V-J Day (Victory over Japan Day). So they wouldn't have to invade mainland Japan. 2  The US dropped the Atom Bomb on Hiroshima after the sneak attack on Pearl Harbor during WWII. 3  It was the first Atom Bomb to ever be used, and was not the last.