Under the unlucky rule of Duke Frederick Ulrich of Brunswick, Calvörde was devastated by Imperial troops in the Thirty Years' War, until it passed into the allodial possessions of his wife Duchess Anna Sophia. Entirely surrounded by Brandenburg-Prussian territory from 1680, the Calvörde exclave by resolution of the 1815 Vienna Congress became part of the newly established Duchy of Brunswick, the Free State of Brunswick after the German Revolution of 1918–19. After World War II, however, according to the 1945 Potsdam Agreement, it fell with the Prussian Province of Saxony to the Soviet occupation zone and from 1949 was part of East Germany.