McCarthy's aim with Blood Meridian was as much about building a historical narrative as retelling actual events within a fictional world. He exaggerated a number of things, including some of the brutal aftermath of battles in the west. I'm not personally aware of any stories about Native Americans systematically raping fallen enemies as he portrays the Comanche as doing. They preferred to scalp, and kill them. It was the women who were raped and we have no end to the stories of that. Americans did enter Mexico for the purpose of hunting natives, as Mexicans did in the US. There was a genocidal system of bounties on the heads of certain native groups that allowed bounty hunters to redeem scalps for cash. Given how difficult warriors were to hunt, a number of the bounty hunters found it easier money to raid a village pretending to be Apache or Comanche and taking the scalps of the dead for payment.

Thanks for the answers!

It's wierd to think that it wasn't that long ago that even western cultures thought in a way that today is represented and common in more brutal and undeveloped parts of the world. The whole "Manifest Destiny" idea is very absurd just 100-150 years later. But I guess that was just the way the world worked back then and I am glad that we have progressed as culture since then to see that this behavior and conduct is unacceptable. Even though it still happens. If there is one positive thing capitalism has given us, then that is making wars obsolete.