Final answer:
The Manhattan Project was a top-secret endeavor in WWII aimed at creating the first atomic bomb, involving over 100,000 people and led to the bombings of Hiroshima and Nagasaki.
Step-by-step explanation:
The Manhattan Project was a top-secret research project initiated during World War II with the goal of developing the first atomic bomb. Over 100,000 people were involved in various capacities, from mining to scientific research. The efforts culminated in the first atomic explosion in July 1945 at the Trinity test site in Alamogordo, New Mexico. The Manhattan Project led to the subsequent bombing of Hiroshima and Nagasaki in Japan, marking the first use of nuclear weapons in warfare and drastically changing the course of the war and global politics.
J. Robert Oppenheimer, a physicist, was chosen to lead the project, and critical breakthroughs, such as the first self-sustained nuclear reactor achieved by Enrico Fermi and his team, paved the way for the development of the atomic bomb.
The enormity of the project and its effects could perhaps be encapsulated in the words of Oppenheimer himself, who quoted from Hindu scripture after witnessing the Trinity explosion: "Now I am become death, the destroyer of worlds." The decision to employ nuclear weapons was fraught with ethical debates but was ultimately justified by U.S. leaders and military officials as a means to end the war with fewer casualties than a conventional invasion would have caused.