Complex sentence: The House of Oldenburg is a North German dynasty and one of Europe's most influential Royal Houses with branches that rule or have ruled in Denmark, Russia, Greece, Norway, Schleswig, Holstein, Oldenburg and Sweden.
Split into simpler sentences: The House of Oldenburg is a North German dynasty and one of Europe's most influential Royal Houses. Branches of the House of Oldenburg rule or have ruled in Denmark, Russia, Greece, Norway, Schleswig, Holstein, Oldenburg and Sweden.