Not content with the stereotypes in Injun Trouble, Bob Clampett remade the cartoon in color as Wagon Heels.
Palefaces keep off lawn.
Porky Pig and his horse sneak across the line, which indicates he knows he's doing something wrong. Later the wagon train "choo-choos" across Indian territory. Although the cartoons portray the Indian as the aggressor, he's actually defending his land against enemy invasion.
Propaganda via cartoons
Despite the jokes, we can see several elements of the Manifest Destiny myth in these cartoons:
1) Indians were savages, killers, beasts--not civilized people with inalienable human rights.
2) Americans were interested only in the abstract notion of "progress," which involved going west but not invading foreign territory, breaking laws and treaties, or killing the land's inhabitants.
3) Americans somehow removed the Indians benignly (perhaps escorting them to reservations) or stood by as they mysteriously vanished. No Americans participated in the conquest, subjugation, or elimination of Indians (i.e., genocide).
Why do Americans believe what they believe about Indians? Because they grew up seeing the same message over and over in textbooks, Western movies, and cartoons such as these. If anything is more ubiquitous than a Warner Bros. cartoon in modern US history, I'm not sure what it is.
For more on the subject, see Native Videos and Cartoons.