For over a century, the Principality of Andorra has been co-ruled by the Spanish Bishop of Urgell and the President of France. How did this strange tag team wind up princes of a tiny mountainous nation? During the 10th century, when Charlemagne fought back the Moorish invaders of Spain, the Andorran men of the mountain came to his aid. In return, the king made Andorra a sovereign principality under the nearby Count of Urgell's rule. So grateful were the Andorrans that most of their national anthem is still about how awesome Charlemagne is. That, and some very dated opinions about Muslims.
But that was the last time the Andorrans had any luck with foreign rulers. The counts of Urgell soon became bored with having to take care of Andorra. In 988, they traded the principality with their local Bishop in an epic bout of feudal swapsies. Needing an army to defend his new princedom, the Bishop of Urgell made a deal with the Lord of Caboet to enter into a partnership of co-rule or, as the French call it, pareage.