Queen Margaret of Denmark joins Sweden, Denmark, and Norway into a single realm under her grandnephew, Eric of Pomerania, by the Treaty of Kalmar, signed on June 17, 1397, in the Swedish castle of Kalmar, on Sweden's southeast coast.

The eternal union stipulates that the Swedish crown shall remain elective and that each country shall retain its own laws and customs.

Although Eric is crowned monarch of all three kingdoms as Erik VII, he remains merely a figurehead for his powerful grandmother, who has dominated Scandinavian affairs, quelled internal violence in Sweden, expanded the royal domain, brought the dukes of Schleswig and Holstein in line, patronized religious institutions, and fostered Danish influence. (The Union of Kalmar, which will last nearly throughout the age, will in fact never formally be dissolved—some argue that its conception was never actually ratified, either. It has been doubted that several of the signatories were personally present—for example, the entire Norwegian "delegation"—and it has been argued that the Treaty was only a draft document. Norway and her overseas dependencies, however, will continue to remain a part of the realm of Denmark-Norway under the Oldenburg dynasty for several centuries after the dissolution.)