January 27, 1942: President Franklin D. Roosevelt authorizes the Manhattan Project, a top-secret research and development program to create an atomic bomb.
July 16, 1945: In the Potsdam Declaration, the United States, the United Kingdom, and China demand that Japan surrender unconditionally or face "prompt and utter destruction."
August 6, 1945: The Enola Gay, a B-29 Superfortress bomber, drops an atomic bomb code-named "Little Boy" on the city of Hiroshima, Japan. The explosion instantly kills an estimated 80,000 people and decimates the city.
August 9, 1945: Despite the Hiroshima bombing, Japan does not surrender. The United States drops a second atomic bomb, code-named "Fat Man," on the city of Nagasaki. The explosion kills an estimated 40,000 people.
August 14, 1945: Emperor Hirohito announces Japan's surrender, effectively ending World War II.