>>1924068>>1925917Spanish traded em to plains natives on their northern frontier
Most plains natives used them for meat and cargo pulling
Few mastered the ability to ride
The down and out/low in the hierarchy Comanche learned how to breed for speed, and learned to ride and fight while mounted (not a thing in modern warfare at the time, the strat was to dismount and fire your already barely accurate firearms)
Commanche then went on a century long vengeance spree murdering basically everyone who wasnt commanche or kiowa.
That 100 years of commanche empire is where all the "natives ride horses" tropes come from. Pretty much every other tribe either didn't ride, or rode poorly.