The significance of the Manhattan Project in World War II lies in its decisive development of nuclear weapons, fundamentally altering warfare and international relations. Launched in 1942, the Project mobilized scientific expertise and resources to lead to the creation of the atomic bomb. The successful testing of the bomb in July 1945 dramatically impacted the war efforts in Japan, leading to the bombings of Hiroshima and Nagasaki in August 1945. This not only forced Japan's surrender, effectively ending World War II but also initiated the nuclear age, raising ethical questions about warfare and power and shaping global geopolitics for decades to come.