The global event marked by the dropping of atomic bombs on Hiroshima and Nagasaki is World War II. The United States dropped the first atomic bomb on Hiroshima on August 6, 1945, and a second bomb on Nagasaki three days later, on August 9. These bombings led to Japan's surrender on August 15, 1945, effectively ending the war. The event is significant for its demonstration of devastating military technology and raises complex moral questions about warfare and the use of nuclear weapons.