The atomic bombings of Hiroshima and Nagasaki were nuclear attacks at the end of World War II against the Empire of Japan by the United States ordered by the U.S. President Harry S. Truman on August 6 and 9 , 1945 . The bombs killed as many as 140,000 people in Hiroshima and 80,000 in Nagasaki by the end of 1945 . During the final stages of World War II in 1945 , the United States conducted two atomic bombings against the cities of Hiroshima and Nagasaki in Japan , the first on August 6 , 1945 and the second on August 9 , 1945 .