Starting in the 12th century, the Margraviate, later Electorate of Brandenburg was in conflict with the neighboring Duchy of Pomerania over frontier territories claimed by both Brandenburg and Pomerania, and over the status of the Pomeranian duchy, which Brandenburg claimed as a fief, whereas Pomerania claimed Imperial immediacy. The conflict frequently turned into open war, and despite occasional success, none of the parties was able to prevail on a sustained basis until the House of Pomerania died out in 1637. While Brandenburg by then would naturally have prevailed, this was hindered by the contemporary Swedish occupation of Pomerania, and the conflict continued between Sweden and Brandenburg-Prussia until 1815, when Prussia was able to incorporate Swedish Pomerania into her Province of