Political correctness definitely isn't the right description for what was a trope born out of white people drawing on stereotypes of the indigenous peoples as terrible savages to provide cover for their own brutalities. One of the most famous examples of this, and at least partially the source of the enduring trope in play here, was the Mountain Meadows Massacre.

/u/sunagainstgold has written about this in the past here and specifically touches on the 'trope' aspect, and /u/quickspore has also written on the topic in the past in this thread.

I'd also point here where I wrote about the use of 'Indian' garb during the Boston Tea Party, although that was intended to lean into different tropes, being grounded in nativist ideas of liberty popular in the colonies during the period. No one expected their rudimentary disguises would actually make anyone think they were Mohawks, the closest settlement being hundreds of miles away.