Questions on the film...

After viewing the film Reel Injun I was left with a few questions concerning the representation of Native Americans in American film. First off, was it during the World War II era, which they said Native American's were being discriminated against in films and propaganda? I thought they said WWII? Anyways I'm wondering why the American film industry needed a target group to discriminate against in the first place? I know it was mentioned in either the reading or the film that Native American discrimination was similar to that of African American discrimination. Why did they move from one ethnic group to another, merely discriminating against because they are different? I'm also left a little confused because although depictions of Native American's were inaccurate throughout American film, in the early years of American film they were not portrayed as the enemy, and as time went on Native's were portrayed as the savage enemy.