Final answer:
Pastoral nomads were migratory groups living on the fringes of early civilizations, herding animals in search of grazing lands. Horticultural societies were the first to have permanent residents due to the cultivation of plants. Plains groups reverted to nomadism with the reintroduction of the horse in North America, which changed their subsistence strategy from agriculture to following bison herds.
Step-by-step explanation:
On the fringes of the first civilizations were pastoral nomads who were migratory groups that herded animals. These migratory pastoralists were people who tended to herds of animals such as sheep, cows, horses, and reindeer. Their livelihood depended on finding new pastures for their animals to graze, which often required seasonal relocations. This way of life made them difficult for states to control as they had little regard for borders and were tough to tax.
The first societies to have permanent residents were horticultural communities. Horticultural societies began when humans started to grow and cultivate their own plants, establishing more fixed settlements.
Plains groups transformed from agriculturalists to nomadic hunter/gatherers in part due to the reintroduction of the horse to North America. The horse greatly enhanced their mobility and transformed their way of life from settled agriculture to following the migrations of bison herds over great distances.