In August 1945, the United States dropped two atomic bombs on the Japanese cities of Hiroshima and Nagasaki, respectively. These were the first and, to date, only uses of nuclear weapons in armed conflict. The bombs, developed under the secret Manhattan Project, caused unprecedented destruction, killing over 200,000 people—mostly civilians—due to the initial blasts and long-term radiation sickness. The U.S. argued the bombings were necessary to force a quick Japanese surrender and avoid a costly ground invasion of the Japanese home islands. Six days after the bombing of Nagasaki, Japan announced its surrender, officially ending World War II. The event remains one of the most debated in history, raising profound ethical questions about the use of weapons of mass destruction and initiating the global nuclear arms race of the Cold War.