Teutonic Order

State · 1236–1525 CE · at its largest around 1402 CE

German crusading military order that conquered Prussia and ruled a monastic state from Marienburg until its grand master secularised it as the Duchy of Prussia in 1525.

On its lands while it lasted

Battle on the Ice (1242 CE): Forces of Novgorod under Alexander Nevsky defeated the knights of the Livonian Order on frozen Lake Peipus.
Klaipeda (1252 CE): Capital of Kingdom of Prussia (1707–1708).
Kaliningrad (1255 CE): Capital of Duchy of Prussia (1526–1618).
Königsberg (1255–1945 CE): Capital of Duchy of Prussia (1526–1618), Brandenburg-Prussia (1619–1701).
Malbork Castle (1274 CE): Brick castle begun by the Teutonic Knights in 1274, later the order's headquarters; the largest castle in the world by land area.
Kernave (c. 1279 CE): Capital of Grand Duchy of Lithuania (1279–1321).
Trakai (c. 1321 CE): Capital of Grand Duchy of Lithuania (1321–1323).
Union of Krewo (1385 CE): Agreement for Grand Duke Jogaila of Lithuania to marry Queen Jadwiga of Poland, uniting the two states and leading to Lithuania's conversion to Christianity.
Kalmar Union (1397 CE): Union of the crowns of Denmark, Norway and Sweden under a single monarch, created under Margaret I and lasting until 1523.
Battle of Grunwald (1410 CE): A Polish-Lithuanian army defeated the Teutonic Knights in one of the largest battles of medieval Europe.
Nicolaus Copernicus (1473 CE – 1543 CE): Polish astronomer and canon of Frombork in Royal Prussia who proposed a Sun-centred model of the universe in De revolutionibus orbium coelestium, published in 1543, the year of his death.
Stockholm Bloodbath (1520 CE): In November 1520 Christian II of Denmark had some 80 to 100 Swedish nobles and clergy executed in Stockholm. The massacre fuelled the revolt that ended the Kalmar Union for Sweden.