It was at one point a fully-fledged country, now it's listed by the UN as an "occupied territory". i.e. Morocco invaded and have taken over. They're adamant it's simply Morocco, and they get really mean to anyone that says otherwise, or even if you have a map that shows it as a separate country.
Driving through it's just like you never left Morocco, except there are military roadblocks every 100km, there is a lot of new construction, and gas is noticeably cheaper than the rest of Morocco (i.e. Morocco attempting to spur development and help "claim" it)
It's fascinating to me a country can be invaded and occupied by their neighbor and the world does nothing about it.