The term "Holstein-Gottorp" refers to a historical duchy in northern Europe, specifically in what is now part of Germany. It was formed in the 16th century when the Duchy of Holstein and the Duchy of Gottorp were united under a single ruler. This region played a significant role in the politics of northern Europe, particularly during the Thirty Years' War. The Holstein-Gottorp dynasty produced several notable rulers, including King Frederick IV of Denmark and Peter the Great of Russia, who married into the family. The duchy was influential in the development of trade and culture in the Baltic region, contributing to the area's historical significance.