Complex sentence: Gottorp is also the name of the ducal house, which rose to several thrones, which means that genealogists and historians call sometimes certain dynasties of some other places with name Holstein-Gottorp.
Split into simpler sentences: Gottorp is also the name of the ducal house, which ascended to several thrones. For this reason genealogists and historians sometimes refer to certain dynasties of other countries with name Holstein-Gottorp.