Short answers, pulled from the story.
The Teutonic Knights invaded Pomerelia in 1308 under a false pretext to help King Władysław I Łokietek. This invasion led to the Slaughter of Gdańsk which marked the beginning of centuries of conflict between Poland and the Germanic order.
Frederick the Great seized Royal Prussia during the First Partition of Poland in 1772 to create a land connection between Pomerania and East Prussia. The province of West Prussia was officially established the following year from these newly acquired lands.
Most of the pre-war territory covering sixty-two percent of land area went to the Second Polish Republic or Free City of Danzig. Fifty-seven percent of the population resided in these newly assigned areas while parts remaining in western Germany formed Grenzmark Posen-West Prussia in 1922.
Nazi forces invaded the region in 1939 and established Reichsgau Danzig-West Prussia. Between 120,000 and 170,000 Poles and Jews were removed through expulsion or massacres with many victims enslaved or killed in extermination camps like Stutthof concentration camp.
Popes ordered the return of Danzig and surrounding lands multiple times yet the Teutonic Knights refused compliance. These disputes sparked a series of wars throughout the fourteenth and fifteenth centuries despite papal intervention.