The Union of Kalmar was a series of agreements that united the kingdoms of Denmark, Norway, and Sweden under a single monarch from 1397 to 1523. It aimed to strengthen the three kingdoms against external threats and to promote trade and cooperation. The union was established by Margaret I of Denmark, who was instrumental in bringing the kingdoms together. Despite its initial success, the union faced challenges due to regional conflicts and power struggles. Sweden eventually sought independence, leading to the dissolution of the union in 1523. The Union of Kalmar remains a significant historical event in the history of Scandinavia.