The Prussian Crusade was a series of 13th-century campaigns of Roman Catholic crusaders, primarily led by the Teutonic Knights, to Christianize under duress the pagan Old Prussians. Invited after earlier unsuccessful expeditions against the Prussians by Polish duke Konrad I of Masovia, the Teutonic Knights began campaigning against the Prussians, Lithuanians and Samogitians in 1230.

By the end of the century, having quelled several Prussian uprisings, the Knights had established control over Prussia and administered the conquered Prussians through their monastic state, eventually erasing the Prussian language, culture and pre-Christian religion by a combination of physical and ideological force.

In 1308, the Teutonic Knights conquered the region of Pomerelia with Danzig (modern-day Gdańsk). Their monastic state was mostly Germanised through immigration from central and western Germany, and, in the south, it was Polonised by settlers from Masovia.

The order, emboldened by imperial approval, quickly resolved to establish an independent state, without the consent of duke Konrad. Recognizing only papal authority and based on a solid economy, the order steadily expanded the Teutonic state during the following 150 years, engaging in several land disputes with its neighbors.