That’s one of the great myths propagated by liberal educators (that’s most of them) for the past fifty years. The idea that the noble original inhabitants were just as bloodthirsty as the nasty, white Europeans is an abhorrent thought to the libs. So they had to concoct a story about all Indians being at one with nature and their Indian neighbors. In reality, many American Indian tribes, like the Sioux, were as happy to slaughter their neighbors and take their lands as were Europeans.
When the Spanish brought horses to their rancheros in what is now Mexico, the natives learned how to wrangle and raise horses. The spread of the horse culture in the Southwest started about 1750 or so and finally reached the Sioux in Minnesota about 1830.
The natives then created the idea that stealing horses was a sign of strength and war prowess, akin to the theft of cars today by gangs.
For more info, search ‘when did Indians get horses?’ or read contemporary accounts of native life in books on Washakie, Geronimo, Red Cloud, Black Elk.
What they didn’t have was a sustainable culture. They were faced by Europeans who’d moved well past the stone age.