Albert Einstein Einstein did not return to Germany. He settled in the United States and became an American citizen in 1940. On the eve of World War II, he endorsed a letter to President Franklin D. Roosevelt alerting him to the potential development of "extremely powerful bombs of a new type" and recommending that the US begin similar research. This eventually led to the Manhattan Project. Einstein supported the Allies, but he generally denounced the idea of using nuclear fission as a weapon. He signed the Russell–Einstein Manifesto with British philosopher Bertrand Russell, which highlighted the danger of nuclear weapons. He was
Siegbert Einstein by the Nazis in 1938). Einstein planted a weeping willow in 1951, and the space was opened to the public. Today the space belongs to Jost Einstein, Siegbert's grandson, who is the director of the Center for Nature Conservation of Bad Buchau. After the end of the war, Siegbert married Elsa Schlittler; because she was an Aryan, Siegbert had additional privileges under the Nazis. They had two children, Rolf Einstein and Kurt Einstein, who were raised Protestant Christians. He was a distant relative of Albert Einstein. He died on December 24, 1968 at the age of 79 and was the