Pomerelia (Ger. Pomerellen, Pol. Pomorze Wschodnie or Pomorze Gdanskie) was the eastern part of medieval Pomerania, extending from the river Leba to the Vistula, with its capital at Danzig (mod. Gdansk, Poland). It bordered on Prussia to the east and medieval Poland to the south, and was occupied by the Teutonic Knights in the course of the Baltic Crusades.
Pomerelia was annexed to the early medieval Polish state by Prince Mieszko I around 950 and regained its independence after the death of King Mieszko II of Poland (1034). It was captured again by Prince Boleslaw III Krzywousty of Poland (d. 1138), who established a new bishopric in Kruszwica. Around 1180 the Polish senior prince Kazimierz II appointed Sambor I (d. before 1209) as ruler of Danzig, and Bogislaw (d. before 1223) as ruler of Schlawe (mod. Slawno). They founded two separate local dynasties.
Sambor’s successors Mestwin I (d. 1217) and Swantop- ulk (d. 1266) had to defend their land against the pagan Old Prussians. From 1230 Swantopulk supported the Teutonic Knights in their military actions in Prussia, but often took the side of the Prussians against the Teutonic Knights. The last Pomeranian ruler, Mestwin II of Danzig, concluded an agreement with Prince Przemysl II of Greater Poland in 1282 at Kçpno and after the death of Mestwin (1294) Przemysl took power in Pomerelia, which helped him to achieve a royal crown the following year. After the assassination of Przemysl II (1296), Pomerelia was taken over by King Wenceslas (Vaclav) II, king of Bohemia (1278-1305) and Poland (1300-1305).
When Wladyslaw I Lokietek of Poland (d. 1333) was unable to help the Pomeranians against an invasion from Brandenburg in 1308-1309, he asked the Teutonic Knights to defend Pomerelia. They exploited the difficult situation to capture Danzig in November 1308, and by fall 1309 had taken the entire province over by force. After the annexation of this large province, the Teutonic grand master Siegfried von Feuchtwangen moved his headquarters from Venice to Marienburg (mod. Malbork, Poland) in neighboring Prussia. The Teutonic Knights divided Pomerelia into new districts or commanderies (Ger. Komtureien), built several strong castles, and between 1340 and 1360 established fourteen new towns. They also unsuccessfully tried to impose a new church organization in Pomerelia by separating it from the bishopric of Wloclawek (Ger. Leslau). King Kazimierz III of Poland (1333-1370) signed an agreement with the Teutonic Knights at Kalisz in 1343, renouncing his rights to Pomerelia, which became an important element of the territorial state of the Teutonic Order, particularly in respect of trade via Danzig and the Vistula.
Poland regained control over Pomerelia as a consequence of the Thirteen Years’ War (1454-1466). By the peace treaty of Thorn (1466), the province was linked to the kingdom of Kazimierz IV, while retaining a certain amount of autonomy within the Polish Crown. Danzig became the largest and richest town in the country. Pomerelia was annexed by Prussia in 1772 after the first partition of Poland and became the new province of West Prussia.