Even after the First World War, the Rhine Province, and thereby Boppard too, belonged to Prussia. Between 1919 and 1923, there were efforts throughout the Rhineland to separate from Prussia, but they were unsuccessful. The National Socialists’ election to power in 1933 brought Boppard no changes at first, as the Centre Party had won 50% of the vote at the 1933 elections. However, on Kristallnacht (9–10 November 1938), the Nazis destroyed the synagogue on Binger Gasse (lane), which had been opened in 1867. Many Jews were seized, and some were sent to concentration camps. Roughly two thirds of the 100 or so Jews living in Boppard emigrated. Those that remained were deported in 1942. In 1940, the Marienberg Convent and its associated school were closed under pressure from the régime. Although Boppard was not the main target of any air strike, bombs were nevertheless dropped on the town. Beginning on 19 March 1945, the Rhine's left bank was controlled by United States forces, who built an emergency bridge across the Rhine at Boppard.