The Polish–Lithuanian–Teutonic War or Great War occurs between 1409 and 1411, pitting the allied Kingdom of Poland and Grand Duchy of Lithuania against the Teutonic Knights.

Inspired by the local Samogitian uprising, the war begins by Teutonic invasion of Poland in August 1409.

As neither side is ready for a full-scale war, Wenceslaus, King of the Romans, brokers a nine-month truce.

After the truce expires in June 1410, the military-religious monks are decisively defeated in the Battle of Grunwald (Tannenberg), one of the largest battles in medieval Europe.

Most of the Teutonic leadership is killed or taken prisoner.

While defeated, the Teutonic Knights withstand the siege on their capital in Marienburg (Malbork) and suffer only minimal territorial losses in the Peace of Thorn (1411).

Territorial disputes last until the Peace of Melno of 1422.

However, the Knights never recover their former power and the financial burden of war reparations causes internal conflicts and economic decline in their lands.

The war shifts the balance of power in Eastern Europe and marks the rise of the Polish–Lithuanian union as the dominant power in the region.