Kalmar Union

State · 1402–1525 CE · at its largest around 1482 CE

A personal union of the kingdoms of Denmark, Norway and Sweden under one monarch, formed at Kalmar in 1397 under Margaret I, and weakened by repeated Swedish revolts.

On its lands while it lasted

Königsberg (1255–1945 CE): Capital of Duchy of Prussia (1526–1618), Brandenburg-Prussia (1619–1701).
Hanseatic trade route (1356–1669 CE): The Hanseatic League of north German merchant towns, led by Lübeck, dominated Baltic and North Sea trade from London and Bruges to Novgorod, exchanging furs, wax, grain, fish and timber for cloth and salt.
Uppsala (c. 1402 CE): Capital of Kalmar Union (1402–1436).
Roskilde (c. 1402 CE): Capital of Kalmar Union (1402–1443).
Battle of Grunwald (1410 CE): A Polish-Lithuanian army defeated the Teutonic Knights in one of the largest battles of medieval Europe.
Wars of the Roses (1455–1487 CE): Civil wars between the houses of Lancaster and York for the English throne, ending with the rise of the Tudor dynasty.
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.