Photo: Albert Einstein Archive, © The Hebrew University of Jerusalem

While watching a German military parade in the 1880s with his parents, young Albert became terrified by the almost mechanical movements of the soldiers who seemed to have no minds of their own. His parents had to promise their frightened son he would never have to become a soldier. Einstein despised militarism and the use of force his entire life—although he later recognized that in some situations, there is no alternative but to "fight for peace."

Einstein denounced World War I and after the war became an outspoken pacifist. But the rise of Nazism and the horrifying events of World War II forced him to reconsider his anti-war position. Concerned the Nazis were building an atomic bomb, he urged the United States to build one first. Six years later, when the bomb was dropped on civilians, Einstein openly regretted his action and became a champion of nuclear disarmament for the rest of his life.