In the late 1930s, American physicists feared German scientists were developing an atomic bomb. They had little doubt Adolf Hitler would use such a weapon if he had it. His bomb and rocket attacks on London killed more than 10,000. So in a very real sense, the scientists believed the future of the free world depended on building an atomic bomb first. The Japanese With Germany's 1945 surrender, and the knowledge it had not successfully built a bomb, some argued the United States should not use the atomic bombs it was building.
Some historians now view that estimate as fanciful, but it seemed believable at the time.
In March 1945, more than 6,000 Marines died taking the barren island of Iwo Jima off the Japanese coast. Days after atomic bombs were dropped on Hiroshima and Nagasaki, Japan announced its surrender. The Cold War Few events of the time startled and angered Americans more than the first Soviet nuclear bomb blast in August 1949. Abruptly, American safety and ascendancy in the world was no longer assured. A hostile country had gained the ability to annihilate our cities.