Ducal Prussia was between (1525–1657) a fief of Poland, created as a result of war (1520–1525) between Poland and the Teutonic Order. Ducal Prussia is a synonym for the Duchy of Prussia (1525–1701), emphasizing that two Prussias existed beside each other: Royal Prussia and Ducal Prussia. Royal Prussia was held by the king of Poland, who also was the feudal lord of Ducal Prussia.
During the Reformation endemic religious upheavals and wars occurred, and in 1525, the last Grand Master of the Teutonic Knights, Albert of Prussia, a member of a cadet branch of the house of Hohenzollern, resigned his position, became a Protestant and received the title "Duke of Prussia" from the Polish king Sigismundus I the Elder in the act called Prussian Tribut. In a deal partially brokered by Martin Luther (under imperial ban since 1521), Ducal Prussia became the first Protestant state, along the lines of the later religious Peace of Augsburg. When the duke Albert of Prussia died in 1569, his son Albert Frederick and then Joachim II Hector inherited Prussia.
The second Treaty of Thorn (1466) had left eastern Prussia as a fief of the Polish crown. In 1660, after the Second Northern War between Sweden, Poland and Brandenburg, the Treaty of Welawa (Wehlau) granted full sovereignty to Frederick William I, the "Great Elector", of the Brandenburg Hohenzollerns as "Duke of Prussia". Thus Ducal Prussia lost its status as a Polish fief and became a part of Brandenburg-Prussia, but not part of the Holy Roman Empire of German Nation. So Elector Friedrich III of Brandenburg could become "king in Prussia" without offending the German king .
After Germany was defeated in World War II and sanctioned by the Potsdam Conference, the southern two thirds of East Prussia was annexed by Poland, the northern part by the Soviet Union. Most of its ethnic German population had then already fled westwards in the last winter of the war, the remaining population was expulsed after the war and Polish and Russian population settled in the now Polish and Soviet territory.
- Royal Prussia
- Kingdom of Prussia
- History of Poland
- East Prussia
- West Prussia
- Detailed Map of Prussia from about 1635 containing Ducal and Royal Prussia (in German)