This article examines the evidence surrounding the U.S.'s warning to Japan before the atomic bomb was dropped on Hiroshima and Nagasaki in August 1945. It discusses the Potsdam Declaration issued by President Truman which called for Japan's unconditional surrender, as well as Japan's response to it and their subsequent decision not to invade mainland Japan. The article also looks at America's warning to Japan prior to the bombing, which has been criticized for its vague nature and lack of specifics about what would happen if they did not surrender unconditionally. Finally, it concludes that whether or not these warnings were effective in alerting Japanese citizens remains an unanswered question.