Horses were incredibly vital for the conquistadors victory against the Inca the most powerful tribes in North America at the time.
Horses impacted the surplus food and population because horses are super strong. People would attach horses to plows and it made farming so much easier and faster. That made huge surpluses and huge populations and huge civilizations.
Horses impacted weapons because people would put on there armor and grab there sowrd but then they would hop on a horse. Horses that are used for military purposes are called Calvary. Calvary is a huge advantage if you are an a horse pretty much know one can get you and you can get every one on the ground. You can also see much further on a horse horses can also trampled other people.
Horses came to America by the Columbus in 1492 now there are 9 million horses in the us.
Sources: "Horses in the United States." Wikipedia. Wikimedia Foundation, 22 Apr. 2017. Web. 24 Apr. 2017. Pictures from image quest and adobe spark.