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Union of Kalmar

On 20 July, Margaret capitalized on the general rejoicing by publishing the famous Treaty of Kalmar, "a masterly document that sealed the union of Norway, Sweden and Denmark". The date she chose was no coincidence - it was the Feast Day of St. Margaret of Antioch, who like the Lady King herself, was cast off by her father and thrown into prison. The Treaty proposed “everlasting union”, which reflected her dearest ambition, that “all three realms should exist together in harmony and love, and whatever befalleth one, war and rumors of war, or the onslaught of foreigners, that shall be for all three, and each kingdom shall help the others in all fealty...and hereafter the Nordic realms shall have one king, and not several".

Well aware of regional pride and prejudice, Margaret played a careful strategy, assuring her subjects that each state would be governed according to the laws and customs of each, no new laws would be introduced without the consent of the subjects, officials from governors to soldiers would be recruited from the native populations, thus showing her subjects that they would enjoy every benefit of union without any threat to national identity. To weld the united kingdoms still more closely together, Margaret summoned a congress of the three Councils of the Realm to Kalmar in June 1397, and on Trinity Sunday, 17 June, Eric was crowned king of Denmark, Norway and Sweden. The Act of Union resulting from this was never completed. Scholars continue to debate the reasons, but the Union existed de facto through the early 16th century reign of King Christian II, and the union of Denmark and Norway continued until 1814.

A few years after the Kalmar Union, the 18-year-old Eric was declared of age and homage was rendered to him in all his three kingdoms, although Margaret was the effective ruler of Scandinavia throughout her lifetime.