You’re misunderstanding what I’m saying. Yes, there were horses in the US in earlier times, introduced by early Europeans (and yes, they were European horses. American horses went extinct 12,000 years or so ago). Native peoples started buying and breeding their own shorter stature ponies ideal for the region. But the massive overpopulation (and the reason that this is such an issue) came from the release of union cavalry. That would be why the current “wild” horses all resemble mustangs and not the sturdy, shorter stature ponies raised and used by the natives in these regions.

Feral horse populations come from the American Civil War, not from the first instances of Eurasian horses arriving in North America. The Union couldn’t afford to house and feed the massive amounts of cavalry horses they had acquired for the war, so they just let them loose, figuring that they wouldn’t survive. Well, they did and they are literally destroying the environment and killing off the actual native populations out there.