The Habsburg Dynasty
The Habsburg Dynasty was a dominant royal house across all of Europe for many centuries. In addition to ruling Austria for more than six centuries, royal marriages extended their power to Bohemia, Hungary, and even Spain.
The enormous family branched off in many directions. Eventually, it got to a point where their strategic marriages would not increase their power, considering they already ruled most of the major courts in Europe.
It finally came to a point in the late 16th century where the only monarchs left to marry were other Habsburgs. Thus, records indicate rampant incest through most of the Habsburgs’ 200-year reign of Spain in the 16th and 17th centuries.
The powerful Habsburg dynasty finally crumbled in 1700 when King Charles II died with no heirs to take the throne. After generations of inbreeding, historians suggest Charles II was infertile due to congenital deformations, leading to the extinction of the Habsburg bloodline.