The Union of Kreva joins the crown of Poland and Lithuania, and the subsequent marriage of Grand Duke Jogaila of Lithuania and reigning Queen Jadwiga of Poland shifts the balance of power; both nations are more than aware that only by acting together can the expansionist plans of the Teutonic Order be thwarted. Jogaila accepts Christianity and becomes the King of Poland as Władysław Jagiełło. Lithuania's conversion to Christianity removes much of the rationale of the Teutonic Knights' anti-pagan crusades. It is also said that the Ordenstaat loses its raison d'etre at this point.

Jagiello officially converts to Christianity.

The Teutonic Knights invade the converted Christian states of Poland and Lithuania. At this time, the Poles and the Lithuanians have little option but to suffer in silence, for they are militarily  unprepared to confront the power of the Knights.

The Treaty of Salynas is signed between the The Grand Duchy of Lithuania, The Kingdom of Poland and the Teutonic Order as preperation  for a Crusade against the Golden Horde. Control of Samogitia passes to the Teutonic Knights.

The Teutonic Knights, under Grand Master Konrad von Jungingen conquer the island of Gotland and drive the Victual Brothers out of the Baltic Sea.

The Incident of the Maiden of Plèsc. Asked by the Hochmeister Konrad von Jungingen to investigate a horrendous crime committed by a brother Knight, Lothar von Schöenberg is thwarted by the guilty Knights uncle, Friedrich von Wallenrode. The case is eventually dismissed by the newly appointed Hochmeister Ulrich von Jungingen and Lothar von Schöenberg falls into disfavour with his superiors.

Grand Master Konrad von Jungingen dies and is replaced with his brother Grand Master Ulrich von Jungingen.

Uprising in Teutonic-held Samogitia starts. Jagiełło of Lithuania announces that he will stand by his promises in case the Teutons invaded Lithuania. This is used as a pretext, and on August 14, 1409 the Teutonic Grand Master Ulrich von Jungingen declares war on the Kingdom of Poland and Grand Duchy of Lithuania (click on map to enlarge).

15 July.  Battle of Grunewald/Tannenberg. With the death of the German King Rupert III, war breaks out between the Teutonic Knights and a Polish-Lithuanian alliance supported by Ruthenian and Tatar auxiliary forces. The climax of the war is the Battle of Grunewald which sees the complete destruction of the field army of the Teutonic Order.