The early independent Thirteen Colonies of North America were in fact a maritime nation. The vast majority of their people clustered east of the Appalachian Mountains, while the environment of the North American Great Plains west of the range was not suited to Europeans.
It was a typical temperate grassland, suitable for pastoral farming but not for cultivation. The indigenous people were not even nomads; they relied on hunting American bison, and no part of the animal went to waste. The meat was eaten, while the hides were made into tents, robes, and so on. After Europeans brought horses over, the cultures of the indigenous peoples of the Plains and Rocky Mountains changed enormously, because horses made hunting far easier.
North America also had Mustangs, perhaps close relatives of Mongolian horses. They had crossed into the Americas via the Bering Strait during the Ice Age and bred there. Yet they had never been domesticated. Early indigenous people hunted horses alongside bison, causing their numbers to dwindle. By the time they needed domesticated livestock to develop advanced agricultural civilization, the lack of horses prevented them from doing so.
Horses intensified conflicts between tribes, because warriors could cross distances that had once been unimaginable on foot. Long before Europeans arrived, tribes had been slaughtering one another over hunting grounds and other resources.
Fathers all hoped to raise their sons into brave, formidable warriors, and training began very early. To toughen their bodies, boys as young as five or six had to run long distances and swim, and they were often deprived of food and water. At seven or ten, they received their first bows and arrows. By fourteen or fifteen, they became exceptionally skilled riders, as though born masters of horsemanship, even surpassing the Europeans who had brought horses to the Americas.