Albert Einstein reacted to the bombings of Hiroshima and Nagasaki with deep regret and condemnation. Upon hearing the news of the Hiroshima bombing, he reportedly said, "Woe is me," expressing his sorrow

. Although he had written a 1939 letter to President Franklin Roosevelt warning about the potential for Nazi Germany to develop atomic weapons—a letter that helped initiate the U.S. atomic bomb project—Einstein later expressed regret for his indirect role. He stated that had he known the Germans would not succeed in developing the bomb, he would have done nothing

. Einstein was deeply shaken by the devastation caused by the bombs. He publicly condemned the use of atomic bombs against Japan but acknowledged that he could not prevent the decision once it was made

. He also used the event to advocate for peace, stating that "the time has come now, when man must give up war" and that it was no longer rational to solve international problems through war

. Following the bombings, Einstein proposed the formation of a world government to control nuclear weapons and prevent future nuclear conflict

. In private correspondence, Einstein defended himself against criticism regarding his role in the development of nuclear weapons, emphasizing his pacifist beliefs and the complex moral circumstances of the time. He acknowledged that while he was a convinced pacifist, he believed the use of force was justified against Nazi Germany, but not for the atomic bombings of Japan

. In summary, Einstein's reaction combined profound sorrow, regret for his indirect involvement, condemnation of nuclear warfare, and a strong call for international peace and disarmament.