The Kalmar Union was a series of personal unions that united the kingdoms of Denmark, Norway, and Sweden under a single monarch from 1397 to 1523. It aimed to strengthen the Nordic countries against external threats and to promote trade and cooperation among them. Despite its initial success, the union faced internal conflicts and power struggles, particularly between Sweden and Denmark. The union ultimately dissolved in the early 16th century, leading to the emergence of independent kingdoms and shaping the future of the Nordic region.