The identity of the citizens of Royal Prussia was fundamentally formed and influenced by their struggle against their masters for two centuries: the Teutonic Knights. The crusading mission of the Knights increasingly lost its primary purpose when, by the fourteenth century, they had largely completed the subjection, Christianisation and assimilation of the pagan Prussians. The Lithuanians, the next target for conquest by the Order, preemptively adopted Christianity when their grand duke Jagiello married the successor to the Polish throne, Jadwiga, in 1385. Dissent and internal strife not only spread among the members of the Order but also marred the relationship between the Knights and their subjects, many of whom had followed in the Order's wake as colonists from North-West Germany. These settlers depended on the Order – by far the largest and most powerful landowner in Prussia – for favours and the distribution of lands, but the Knights' increasingly arbitrary style of government triggered a new sense of political, economic and cultural solidarity among the Prussian townsmen and landed freemen.

The first corporate bodies, foreshadowing the future organisation of estates and regular diets, originated in assemblies set up from the mid-fourteenth century by the Hanseatic towns Thorn, Kulm, Danzig, Elbing, Königsberg and Braunsberg, under the watchful eye of the Order. The Lizard League, the first organised body of the provincial nobility, was founded in 1397 and voiced its opposition on matters such as taxation and land administration.