It's typically called a 'going native' story. Person from comparatively advances society goes back to a simpler way of life, realises that everything he thought he knew was wrong, and living off the land is the way to go.
Even when The Mission was first released, the idea was nothing new.
Never defend crap with 'It's just a movie'
http://www.youtube.com/user/BigGreenProds

The Mission was made in 1986, way before Dancing with Wolves.
Hence, why he said "The Mission is a
Proto
-Dances with Wolves."
~ I've been very lonely in my isolated tower of indecipherable speech.

The Mission was made in 1986, way before Dancing with Wolves.

A Man Called Horse is really the proto-Dances with Wolves.