In the aftermath of World War II, the United States established the Atomic Energy Commission (AEC) to oversee the development and regulation of nuclear energy. The AEC was responsible for managing the legacy of the Manhattan Project and ensuring the peaceful use of nuclear technology. It marked the transition from wartime to peacetime nuclear research and development.

Following the bombings of Hiroshima and Nagasaki, Japan announced its unconditional surrender to the Allied Powers, effectively bringing World War II to an end. The surrender was formally signed on September 2, 1945, aboard the USS Missouri in Tokyo Bay. The use of atomic bombs was a significant factor in Japan's decision to surrender.

Three days after the bombing of Hiroshima, the United States dropped a second atomic bomb on Nagasaki, Japan. The bomb, called 'Fat Man,' resulted in the deaths of approximately 70,000 people by the end of 1945. This second bombing contributed to Japan's decision to surrender, effectively ending World War II.

The United States dropped an atomic bomb on the Japanese city of Hiroshima during World War II. The bomb, known as 'Little Boy,' was the first nuclear weapon used in warfare. The explosion caused unprecedented destruction, killing an estimated 140,000 people by the end of 1945 and leading to Japan's eventual surrender.

The Trinity Test was the first detonation of a nuclear weapon, conducted by the United States Army as part of the Manhattan Project. The test took place in the Jornada del Muerto desert in New Mexico. The successful explosion of the plutonium-based implosion-type bomb marked a significant achievement in nuclear weapons development and demonstrated the destructive power of atomic energy.

The Los Alamos Laboratory, also known as Project Y, was established in Los Alamos, New Mexico, as the central site for the design and assembly of nuclear weapons. Under the direction of J. Robert Oppenheimer, scientists and engineers worked to solve the complex problems associated with creating a functional atomic bomb.

The first controlled nuclear chain reaction was achieved under the leadership of Enrico Fermi at the University of Chicago. This experiment, known as Chicago Pile-1, was a critical milestone in the development of nuclear reactors and demonstrated that a sustained nuclear chain reaction was possible, paving the way for the development of nuclear weapons.

The Manhattan Project was officially established as a research and development undertaking during World War II that produced the first nuclear weapons. It was led by the United States with the support of the United Kingdom and Canada. The project was a response to fears that Nazi Germany would develop atomic weapons first.

Albert Einstein and Leo Szilard wrote a letter to U.S. President Franklin D. Roosevelt, warning about the potential for Nazi Germany to develop an atomic bomb. This letter was pivotal in alerting the U.S. government to the potential military applications of nuclear fission, ultimately leading to the establishment of the Manhattan Project.

The discovery of nuclear fission by Otto Hahn and Fritz Strassmann in Berlin laid the scientific foundation for the Manhattan Project. This breakthrough demonstrated that the nucleus of a uranium atom could be split into lighter elements, releasing a significant amount of energy. This discovery was crucial as it opened the possibility of harnessing nuclear energy for both civilian and military applications.