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 them both, 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 prevailed permanently until the House of Pomerania died out in 1637. Brandenburg would by then have naturally have prevailed, but this was hindered by the contemporary Swedish occupation of Pomerania, and the conflict continued between Sweden and Brandenburg–Prussia until 1815, when Prussia incorporated Swedish Pomerania into her Province of Pomerania.
Early medieval prelude
In the 10th century, the area of the future Brandenburg and Pomerania was inhabited by West Slavic tribes, collectively known as Wends. Roughly, the tribes east of the Oder and north of the Warta (Warthe) rivers constituted the Pomeranians and the tribes west of the Oder the Luticians. The classification is uncertain for the tribes living close to the lower Oder, that is the Velunzani on the islands in the Oder estuary, the Prissani on the eastern bank of the lower Oder, and the Ukrani and Recani on the western bank of the lower Oder, which became known as the Uckermark.Kirsch (2004), pp. 73, 74
The tribes west of the Oder were organized in marches of the Ottonian (Liudolfing) realm, which became the Holy Roman Empire with the coronation of Otto I, Holy Roman Emperor in 962. The marches set up in the area of the future Brandenburg and Pomerania were the Billung March in the north, and the Saxon Eastern March in the south; the boundary was the Peene river. The Saxon Eastern March was soon partitioned, with the area of future northern Brandenburg and southwestern Pomerania re-organized in the Northern March. A rebellion of the Liuticians overthrew the margraves' rule in most of the Northern and Billung marches between 983 and 995.Kirsch (2004), p. 74 In the 11th century, the Liutician confederation collapsed due to internal struggles, leaving its territory vulnerable to its neighbors' campaigns,Kirsch (2004), p. 75 including expeditions of the margraves of the Northern March.Robinson (2003), pp. 3–4, 24
House of Ascania vs House of Pomerania Wartislaw I, Duke of Pomerania and first verified member of the House of Pomerania, conquered the Peene and Tollense areas west of the lower Oder from the Luticians during the 1120s. Albert (Albrecht) the Bear, invested with the March of Lusatia in 1123, was ready to succeed deceased Henry, Count of Stade as margrave of the Northern March in 1128,Fuhrmann (1986), p. 122 and was invested with the march by Holy Roman Emperor Lothair of Supplinburg in 1134, after he had already secured his succession of Pribislaw of the Hevelli in 1129.Materna (1995), p. 86 In 1128, Albert participated in the organization of the mission of Otto of Bamberg in the Lutician areas held by Wartislaw I of Pomerania, and supplied him with an escort.Kirsch (2004), p. 76 When in 1136 Emperor Lothair gave lands in the Peene area to Otto's bishopric of Bamberg, Albert was asked to approve first.
Focused on the Northern March, Albert renounced his post as the margrave of Lusatia in 1136, which was then fused into the March of Meißen and became the basis of the state of the House of Wettin.Fuhrmann (1986), p. 123 In 1138, Conrad III of Germany also invested Albert the Bear with the Duchy of Saxony, but Albert resigned in 1142 due to the opposition of the Saxon nobility, who had favoured and eventually installed then minor Henry the Lion as their duke.Barber (2004), p. 188
In 1147, Albert participated in the Wendish Crusade to the Pomeranian strongholds of Demmin and Stettin, which however did not result in the acquisition of territories — the size of the Northern March actually controlled by Albert differed significantly from what Emperor Lothair had originally promised. Instead, as a result of the crusade, several Saxon nobles had established petty realms in the march, and the Pomeranians still held vast areas south of the Peene river as well as the Uckermark. Albert however succeeded Pribislaw in the Hevellian territories in 1150, and when he defeated Jaxa of Köpenick and incorporated the latter's territory into his march in 1157, the term Margraviate of Brandenburg replaced the designation Northern March.Materna (1995), p. 87 Albert upheld his claims to Western Pomerania, and campaigned in the Pomeranian-held Uckermark since 1157.Kirsch (2004), p. 77
Albert the Bear's successor in Saxony, Henry the Lion, had by then established himself as one of the most powerful nobles in Germany.Barber (2004), p. 191 In pursuit of his own interests in the Wendish territoriesRiis (1995), p. 23ff and with Danish support, Henry defeated his rebellious Obodrite subjects and their Pomeranian allies in the Battle of Verchen near the Pomeranian stronghold of Demmin in 1164.Riis (1995), p. 25 As a consequence, the Pomeranian dukes became Henry's vassals,Piskorski (1999), p. 43 and supported Henry in subsequent campaigns against the margraves of Brandenburg.Heitz (1995), p. 167 However, Henry finally lost the struggle he was engaged in with Holy Roman Emperor Barbarossa, and in 1180 was deprived of his ducal titles.Fuhrmann (1986), pp. 169, 175 The Pomeranian duke then pledged allegiance to Barbarossa in 1181,Piskorski (1999), p. 44 thwarting Ascanian ambitions.
Constant Danish military pressure resulted in Danish vassalage of Pomerania in 1184/85. The Ascanian margraves launched several expeditions into Danish Pomerania between 1198 and 1199, and between 1211 and 1214. Despite a temporary sack of Stettin in 1214Piskorski (1999), p. 45 and more permanent territorial gains in the Finow area,Materna (1995), p. 93 they were unable to establish themselves in Pomerania, and Danish superiority even led Frederick II, Holy Roman Emperor to renounce all German claims to the area in favour of Denmark in 1214. By then, the margraves restricted themselves to guard the contemporary Brandenburg-Pomeranian frontier by erecting the Oderberg fortress "contra Sclavos" in 1214. Only after the utter defeat of the Danish forces in the Battle of Bornhöved in 1227, was the area reclaimed by the empire. The Brandenburgian margraves then re-enforced their claims on Pomerania, and were invested with the duchy by Frederick II in 1231 in Ravenna.Buske (1997), p. 18Materna (1995), p. 94
In the 1230s, the Margraviate of Brandenburg was ruled in common by two brothers of the House of Ascania, John I and Otto III, while the Duchy of Pomerania was partially divided and ruled by two cousins of the House of Pomerania, Wartislaw III of Pomerania-Demmin and Barnim I of Pomerania-Stettin. Johann I of Brandenburg married a daughter of Valdemar Sejr, king of Denmark, and therewith came into possession of half of the terra Wolgast in Pomerania. He then forced Wartislaw III into the Treaty of Kremmen in 1236: Wartislaw III had to recognize Brandenburgian overlordship and succession in Pomerania-Demmin, and cede his territories south of Demmin to Brandenburg.
Also in the 1230s, Barnim I had sold the southern Uckermark between Templin and Angermünde to the margraves, and renounced his claims on the Barnim and Teltow areas.Zientara (2002), p. 339 In the subsequent Treaty of Landin (Hohenlandin) in 1250, Barnim I formally accepted Brandenburgian overlordship and ceded the northern Uckermark to Brandenburg, but in turn received Johann's part of Wolgast and managed to rescind the succession clause of Kremmen. Barnim I had to make further territorial concessions when Brandenburg established her Neumark ("New March") along the Warthe (Warta) river in the second half of the 13th century, and in 1267 married Mechthild, daughter of Otto III of Brandenburg.
Barnim I had inherited Pomerania-Demmin after Wartislaw III died without issue in 1264, but the duchy was again internally divided in 1295 – this time into a northern part, Pomerania-Wolgast, and a southern part, Pomerania-Stettin. In 1302, Otto I of Pomerania-Stettin, grandson of Brandenburgian margrave Otto III, made peace with Brandenburg.Heitz (1995), p. 176 Tensions with Pomerania-Wolgast eased when Waldemar became the Brandenburgian margrave in 1309, and Brandenburg pawned Schlawe-Stolp to Pomerania in the Treaty of Templin, concluded in 1317.Heitz (1995), p. 177 With Waldemar's death without issue, the House of Ascania died out.Materna (1995), p. 134