He was a pacifist until Hitler came to power and caused him to revise his geopolitical equations. He urged the building of the atom bomb, but then became a leader in the movement to find ways to control it. Just as he sought a unified theory in science, he sought a world federalism that would impose order on competing nations. His belief in the value of free thought and speech, and his merry willingness to defy authority, caused him to be an adamant opponent of McCarthyism.