Prehistoric horses had been extinct in the United States for more than 11000 years before they were brought over from Spain by settlers who lived mostly in the Southwest. This is why the tribes in the Southwest were some of the first to actually reap the benefits of horses, integrating them into their daily life. In particular, the Plains tribes saw horses as upgrades because they were only using dogs or buffaloes for transportation purposes. In comparison, horses were capable of dragging large amounts of equipment easier and faster.
Once they were introduced, they became a key part of many Native American's daily lives. The tribes adapted horses to fit their own lifestyles - meaning they did mostly the same things they had done before, but they started using horses to make it easier. Horse breeding became important as the tribes wanted to make sure they would have a good supply of horses to perform the tasks of transportation.
Naturally, horse breeding was extremely complicated as well. Native Americans, like people today, bred their horses carefully so that good traits like speed or stamina remained while bad traits like disease or lameness were eliminated. For instance, the Blackfoot tribe bred their horses with one of three characteristics in mind: the horse's color, its size, and its speed. The owner of a mare, or female horse, would select a stallion, or male horse, that had characteristics that he desired. Then he would breed the two together.
Despite what many movies suggest, Native Americans did not breed their horses to attain the white and brown "paint" coat. Most horses were not paints, they were solid! Painted horses would actually stand out against the earth tones of the plains. Many tribes also bred horses to be as strong as possible so that they could carry large loads.
Horse breeding was very important for many tribes as they relied on horses to make their daily life easier. To this day, many Native Americans know as much about horse breeding as other breeders.