I ran across an io9 article from 2011, “Why inbreeding really isnt as bad as you think it is”, which is topical for some of the genetics I’ll be teaching over the next couple of weeks in my introductory course. It has a lot of fun details about historical inbreeding, including the case of Charles II of Spain:
From 1550 onward, not a single outsider married into the Spanish royal line. The result of all this was Charles II, quite possibly the most inbred person in history.
Charles's ancestry was so ridiculously intertwined that he actually had a higher relationship coefficient than the child of two siblings, and 95.3% of his genes could be traced back to just five ancestors. While the previous kings had escaped their already considerable inbreeding relatively unscathed, Charles suffered from massive mental, physical, and emotional disabilities, earning him the nickname El Hechizado, "The Hexed."
The article does a very good job of describing the effects of bottlenecks, concepts like “pedigree collapse” and the consequences of the exponential growth of genealogical ancestors going back in the past.