The official reason given for the use of atomic bombs on Hiroshima and Nagasaki was to expedite Japan's surrender and thus bring a swift end to World War II. U.S. officials believed that a full-scale invasion of Japan would result in significant casualties for both American forces and Japanese civilians. By using atomic bombs on August 6 and 9, 1945, the U.S. aimed to demonstrate overwhelming military power, discourage further resistance, and prevent an invasion that could lead to an extended conflict. Ultimately, these bombings contributed to Japan's surrender on August 15, 1945, marking the end of the war in the Pacific.