The House of Oldenburg is a European royal family that originated in the 12th century in what is now Denmark. It has produced several monarchs and has connections to various royal houses across Europe, including the House of Glücksburg and the House of Schleswig-Holstein. The family played a significant role in the history of Denmark, Norway, and Sweden. Members of the House of Oldenburg have ruled over several territories, including the Kingdom of Denmark and the Duchy of Schleswig. The family is known for its influence in European politics and its intermarriages with other royal families, which helped to strengthen alliances throughout history.