Part of the Einstein exhibition.
Adolf Hitler became chancellor of Germany in 1933, and five weeks later, the Nazis established their first concentration camp. In 1935, the Nazis issued the Nuremberg Laws: "racial purity" laws that stripped German Jews of their citizenship. Violence broke out in November 1938, when Nazis destroyed Jewish businesses, homes, hospitals, and synagogues, killed nearly 100 and arrested some 30,000 Jewish men in what came to be known as Kristallnacht. By 1939, 300,000 Jewish refugees had fled Nazi controlled territories. By the war's end in 1945, six million Jews and millions of other victims had died in the Holocaust.
Einstein learned of the tragic events unfolding in his former country from his new home in the United States. Only a decade earlier, he had argued passionately against war. But now Einstein recognized that war was the only option.
The rise of Nazism in Germany during the 1930s—and the conviction that Hitler could be defeated only by military force—prompted Einstein rethink his strict pacifist views. Increasing numbers of Jewish refugees were fleeing Germany, bringing with them horrific tales of Nazi persecution; Einstein, who was also Jewish, left for the United States in 1932.
When three refugee physicists confided to Einstein that the Nazis might be developing a new weapon—an atomic bomb—he decided to act. Despite his previous appeals for governments to dispense with the weapons of war, Einstein wrote to President Franklin Roosevelt in 1939 alerting him to "a new phenomenon that would...lead to the construction of bombs" and suggested that the United States accelerate its atomic weapons research program. Scholars debate the effect of this letter. Einstein signed it in 1939 and the Manhattan Project, the U.S. effort to build the bomb, began in 1941.