The modern horse was introduced to North America in 1519 by Spanish conquistadors. Hernán Cortés brought 15 horses to the mainland, and many of them were granted to settlers in Mexico and New Mexico. Further expeditions brought more horses, and large, wild herds existed in America by the 17th century.
The evolutionary ancestors of modern horses were present in North America in prehistoric times, but they died out around the time other large mammals, such as the woolly mammoth, began to disappear, which was around 8,000 to 10,000 years ago. Possible reasons for this extinction include excessive hunting by early natives and disease.