During the Thirty Years' War, Swedish forces entered the Duchy of Pomerania in 1630. Greifswald was besieged by Swedish troops on 12 June 1631 and surrendered on 16 June. Gustavus Adolphus of Sweden had returned from Brandenburg to supervise the siege, and upon his arrival received the university's homage for the liberation from Catholic forces. After the Thirty Years' War (1618–1648), Greifswald and the region surrounding it became part of the Kingdom of Sweden. Swedish Pomerania, as it was then called, remained part of the Swedish kingdom until 1815, when it became part of the Kingdom of Prussia as the Province of Pomerania. In 1871, it devolved to Germany.