The movie is based on a true story. US Army scout MacIntosh leads the troops sent out to chase down Apache Ulzana, more commonly known as Josana, who has left the reservation. One of the main characters is an Apache scout, modeled after two or more real Apache scouts, who does his job despite not being fully trusted by the rookie Lieutenant who led the Army detachment.
Ulzana's Raid is said to be an allegory about the Viet Nam War. The pillaging, burning and raping Apaches are equated with the American troops running wild in Viet Nam. But the movie definitely stands on its own as a superb Western.
Although the portrayal of the Apaches can be viewed as a negative one, there are several things that redeem the movie for me. The Apaches are portrayed as intelligent, disciplined fighters. The movie is one of the best at examining Apache tactical maneuvers. It also portrays the Apache scout as a brave and noble person.
Another thing that redeems the movie for me is that the writer was really talking about the savageries being committed in the Viet Nam War, not the Apache wars. One point he is probably making is that all humans can act like savages when they are in certain situations.
I think, but I don't know for sure, that one of the last scenes, in which Ulzana is executed by the Army Apache scout, is a mimicking of the famous picture of the Viet Cong executed by his fellow countryman, the South Vietnamese police chief. In any case the movie does address how some members of the indigenous group join with the invaders against their own people.