After the failed union of Sweden and Norway of 1319–1365, the pan-Scandinavian Kalmar Union was instituted in 1397. The Swedes were reluctant members of the Danish-dominated union from the start. In an attempt to subdue the Swedes, King Christian II of Denmark had large numbers of the Swedish aristocracy killed in the Stockholm Bloodbath of 1520. Yet this measure only led to further hostilities, and Sweden broke away for good in 1523. Norway, on the other hand, became an inferior party of the union and remained united with Denmark until 1814.

When was the Kalmar Union formed?