In the 12th century, Poland, the Holy Roman Empire's Duchy of Saxony and Denmark variously conquered Pomerania, ending the tribal era.

The areas stretching from Kolberg (Kołobrzeg) to Stettin (Szczecin) were ruled by Ratibor's brother Wartislaw I and his descendants (House of Pomerania, also called Griffins, of which he was the first ascertained ancestor) until the 1630s.

[3] The conquest resulted in a high death toll and devastation of vast areas of Pomerania, and the Pomeranian dukes were forced to become vassals of Boleslaw III, King of Poland.

[7] In 1135, Bolesław had accepted overlordship of Holy Roman Emperor Lothair III and in turn received his Pomeranian gains as well as the still undefeated Principality of Rügen as a fief.

[9] With Bolesław's death in 1138 and the fragmentation of Poland, Polish overlordship ended,[10] triggering competition of the Holy Roman Empire and Denmark for the area.

[12] After Wartislaw's Lutician conquests, his duchy lay between the Bay of Greifswald to the north, Circipania, including Güstrow (Ostrów), to the west, Kolobrzeg in the east, and possibly as far as the Havel and Spree rivers in the south.

[17][clarification needed] Also, the territories were invaded by Danish forces multiple times, who, coming from the Baltic Sea, used the rivers Peene and Uecker to advance to a line Demmin–Pasewalk.

[26][28] The direct subordination under the pope thwarted the claims of the archbishops of Magdeburg and Gniezno, who both had asserted pressure on Otto of Bamberg to incorporate the new diocese into their realms.

[41] Germans, at this early stage (before 1240), were often settled in frontier regions, such as the mainland part of the Principality of Rugia (after prince Jaromar I granted Eldena Abbey the right to call in settlers in 1209), Circipania, the lands of Loitz (administered semi-independently by Detlev of Gadebush), the Uckermark, the lands of Kolbatz Abbey and Bahn (which later was granted to the Knights Templar), and the area north of the Warthe and along the lower Oder river.

Before the end of the 13th century, the Western Pomeranian mainland and most of Farther Pomerania west of the Gollenberg had turned almost completely German, mentions of Slavs in documents became exceptional.

In the 1260s followed Wollin (1260), Ueckermünde, Wolgast, probably already Gützkow, Pölitz (1260), Greifenberg (1262), Gollnow, probably already Usedom, Penkun, Tribsees (Principality of Rügen, before 1267) and Naugard (by the bishop of Cammin, before 1268).

The early 14th century saw the foundation of Stolp (by Waldemar of Brandenburg, 1310), Neustettin (by Wartislaw IV, 1310), Rügenwalde (again 1312, the 1270s precursor had not done well), Rugendal (Principality of Rügen, before 1313, decayed), Schlawe (by the Swenzones, 1317), Garz (by the princes of Rügen, 1320s), Jacobshagen (by three brothers von Stegelitz, 1336), Freienwalde (by von Wedel, before 1338), Zanow (by the Swenzones, 1343), Lauenburg (by the Teutonic Knights, 1341), Bütow (by the Teutonic Knights, 1346), and Fiddichow (by Barnim III, 1347).

[53] Indigenous Slavs and Poles faced discrimination from the arriving Germans, who on a local level since the 16th century imposed discriminatory regulations, such as bans on buying goods from Slavs/Poles or prohibiting them from becoming members of craft guilds.

[57] The relation between the towns and the nobility throughout the Middle Ages ranged from alliances and support (German: Landfrieden) to cabalism, banditry and outright warfare.

[13] His brother, Ratibor I of Schlawe-Stolp, founded Stolpe Abbey near this site and ruled Wartislaw's realm in place of his minor nephews, Bogislaw I and Casimir I.

Until 1250, Barnim I, Duke of Pomerania had recovered most of the previous Pomeranian territory[68] and sought to secure them with the settlement of Germans, while Zantoch burgh was held by Przemysł II of Greater Poland.

[71] A series of wars was triggered by Denmark in the early 14th century, when Eric VI Menved attempted to reestablish Danish rule in Northern Germany.

[73] To achieve these goals, the dukes allied with various neighboring states, mounted military campaigns of which the first Battle of Kremmer Damm in 1332 was the most important, and gave their lands to the Cammin bishops (in 1320)[74] and even to pope John XXII (in 1330[73][74] or 1331).

[73][75] The towns Stettin, Greifenhagen, and Gollnow in Pomerania-Stettin, concerned about a permanent division of the duchy in case Barnim III would not have children, rebelled in 1339 and sided with Pomerania-Wolgast in 1341.

[76] Barnim III, against the will of the burghers, erected a castle within Stettin's walls in 1346 (the old burgh had been leveled in 1249),[78] and gained from Brandenburg the eastern parts of the Uckermark, that was in 1354 Pasewalk, in 1355 Schwedt, Angermünde, and Brüssow, and in 1359 (Torgelow).

Wartislaw's minor sons were aided by primarily by Greifswald and Demmin, but also by Stralsund, Anklam, and Valdemar III, who decisively defeated the Mecklenburgian army in 1228 near Völschow.

Wartislaw VI received Pomerania-(Wolgast)-Barth, the former principality of Rügen, and Bogislaw IV's Pomerania-Wolgast was reduced to an area between Greifswald and the Swine river.

On 17 May 1373 all dukes of Pomerania concluded an alliance in Kaseburg, but situation eased when Otto VII, Margrave-elector of Brandenburg abdicated on 15 August 1373, and the House of Luxembourg took over the march on October 2 of the same year.

[94] When Wartislaw VII died, Bogislaw VIII and Barnim V concluded a treaty with the Teutonic Knights to safeguard their supply routes in turn for a financial credit.

Also in 1521, Johannes Bugenhagen, the most important person in the following conversion of Pomerania to Protestantism, left Belbuck Abbey to study in Wittenberg, close to Luther.

On 13 December 1534 a Landtag was assembled in Treptow an der Rega, where the dukes and the nobility against the vote of Cammin bishop Erasmus von Manteuffel officially introduced Protestantism to Pomerania.

The Pomeranian dukes Johann Friedrich and Ernst Ludwig refused to pay their taxes to the circle's treasury (Kreiskasten in Leipzig) properly, and in the rare cases they did, they marked it as a voluntary act.

[111] The Pomeranian dukes justified their actions with events of 1563, when an army led by Eric of Brunswick crossed and devastated their duchy, and the circle did not give them support.

[110] Yet, due to the rejection of financial support by the nobility, the Pomeranian dukes' funds for the campaign were low, resulting in their humiliation during the war for fighting with bad horses and weapons.

In the course of the Thirty Years' War, the duchy was occupied first by Albrecht von Wallenstein's mercenary army after the Capitulation of Franzburg in 1627, and then by the Swedish Empire, which was appreciated and confirmed by Bogislaw in the Treaty of Stettin (1630).