Under the scientific leadership of J. Robert Oppenheimer, the Manhattan Project developed the first nuclear weapon. The invention relied on nuclear fission—splitting the nucleus of an atom (Uranium-235 or Plutonium-239) to release a massive amount of energy. The first test, 'Trinity,' occurred in New Mexico, followed by the bombings of Hiroshima and Nagasaki. This invention ended WWII but also initiated the Cold War and the era of 'Mutually Assured Destruction.' It forced a global shift in diplomacy and ethics, and led to the development of nuclear power as a source of civilian energy.