The Cold War was waged between the United States and the Union of Soviet Socialist Republics (USSR). They fought of a war of ideology and propaganda that resulted in the creation of nuclear arsenals still in existence that can destroy the world many times over.
The United States in late 1941 established a secret program, which came to be known as the Manhattan Project, to develop an atomic bomb, a powerful explosive nuclear weapon. The aim of the project, directed by physicist J. Robert Oppenheimer, was to build an atom bomb before Germany did. After Roosevelt's death in April 1945, Harry S. Truman became president and inherited the bomb-development program. At this point, the new weapon had two purposes. First, it could be used to force Japan to surrender. Second, possession of the bomb would enable the United States, and not the USSR, to control post-war policy.
Some would argue that the Cold War began even before World War II ended. Already the United States and USSR were in the midst of carving up the former Axis territories when In July 15, 1945 the United States of America detonated the first Atomic Bomb in New Mexico. It was called the "Trinity" test, exploding with a force equivalent to 18,000 tones of TNT. Later, (July 25), the United States General Carl Spaatz (Commander of the Strategic Air Force in the Pacific in the war with the Japanese), received a directive to drop an atomic bomb in Japan. On August 6, the "Little Boy" atomic bomb exploded approximately 1,900 feet above Hiroshima with a force equivalent to 12,500 tones of TNT. Three days later, on August 9, 1945, the U.S. A-bomb "Fat Man" exploded at around 1,650 feet over Nagasaki with a yield equivalent of 22,000 tons of TNT. Many died (140,000) in Nagasaki and Hiroshima by the end of 1945. Thus, the Nuclear Age and the nuclear arms race that fuelled the Cold War began together. .
Calls by scientists and diplomats for international control and monitoring of nuclear weapons went unheeded.