Answer: North America

If you’re well versed in the (relatively) recent history of the world, you may recall that horses were introduced to the Americas by Spanish explorers. What is often glossed over in those grade school history lessons, however, is that it wasn’t an introduction, but a reintroduction of the species to the Americas.

The oldest fossils of horses and their evolutionary ancestors in the Equus genus are found in the Wind River basin in Wyoming. Yet despite their obvious presence, horses didn’t become an integral part of human culture on the continent until the arrival of the Spanish in the 16th century. Where then, were all the horses?

Approximately 8-12,000 years ago, the native horses were wiped out. While the specific cause of the mass extinction is still debated—one theory posits that ice-age related climate change killed off the grasslands that fed the huge herds of wild horses, another posits that it was the introduction of humans to North America that led to humans killing and eating all of the horses—what is certain is that they vanished in a very short span of time.

In the present, however, horses have made quite a stellar recovery. In the United States alone, there are currently ~9.2 million horses under human care with an additional ~33,000 feral horses roaming free, primarily in the western United States on large swaths of public land managed by the Bureau of Land Management.