The Avatar that Dances with Samari's on Mars
Now I love all these movies but I cannot ignore the similar themes in all these movies. Soldier is sent to a far away place to conquer/study indigenous tribe. Soldier infiltrates the tribe, learns their ways and is assimilated into the tribe, falls in love with one of their women, then goes to war on their side against the very people who sent him!
Similar movies: Avatar, Dances with Wolves & John Carter (of Mars).