sentences:  When discovered on the eve of World War II, this insight led multiple countries to begin programs investigating the possibility of constructing an atomic bomb — a weapon which utilized fission reactions to generate far more energy than could be created with chemical explosives.The Manhattan Project, run by the United States with the help of the United Kingdom and Canada, developed multiple fission weapons which were used against Japan in 1945 at Hiroshima and Nagasaki.During the project, the first fission reactors were developed as well, though they were primarily for weapons manufacture and did not generate electricity.