The Second World War ended in defeat for Germany in May 1945, and with that ended the twelve Nazi years and a national policy driven by anti-Semitism. It also seemed reasonable to assume that the end of the Hitler regime meant an end to one-party dictatorship. The entire central part of what had been Germany, including Leipzig and Castle Thallwitz, now became designated as the Soviet occupation zone: this was part of a larger scheme of border changes and other territorial provisions agreed by the political leaders of the victorious powers at the Yalta Conference. Rosenthal joined the Social Democratic Party (SPD) in 1945.