Royal Inbreeding

Somewhere along the lines, a long time ago, ruling families got the idea that their blood was better than everyone else's, so they wanted keep reproduction in the family, so to speak. This was also a convenient way to keep inherited wealth from being divided. But inbreeding will catch up with you sooner or later, as more and more harmful genes get doubled up. The case we are most familiar with is that of Charles II of Spain, whose family tree was not only a wreath, but even more like an Euler diagram. 

But he was far from the only victim of royal inbreeding. It's been pretty common in Europe. Loony Throne takes us through ten royals in which inbreeding made a lasting mark on history.