Final answer:
The Manhattan Project was the project that developed the American atomic bomb during World War II, led by J. Robert Oppenheimer and prompted by warnings from Albert Einstein to President Roosevelt. It employed over 100,000 people, cost $2 billion, and successfully tested an atomic bomb in July 1945.
Step-by-step explanation:
The project that developed the American atomic bomb during World War II was known as the Manhattan Project. Initiated by the urging of Albert Einstein, the Manhattan Project was a massive, top-secret endeavor with the goal of creating a deliverable atomic weapon. Einstein, who had emigrated from Germany to escape Nazi persecution, played a pivotal role in advocating for the atomic bomb's research by reaching out to President Roosevelt. The project began earnestly following the Japanese attack on Pearl Harbor, accelerating research and development.
Under the direction of physicist J. Robert Oppenheimer, the Manhattan Project pooled extensive resources and talents, including refugee scientists from Europe, and was spread across multiple sites in the United States. The efforts culminated in July 1945 with the Trinity test, the world's first successful detonation of an atomic bomb. Shortly thereafter, in August 1945, this new technology brought a devastating end to World War II with the bombings of Hiroshima and Nagasaki.