At the time of contact with whites, it is believed that the only non-farmers on the Great Plains were the Blackfoot in the North and the Comanche in the South. Most of the region´s other early tribes were villagers and farmers ... As the soil became tired-out in one area, they probably migrated [moved] northward.

(Carl Waldman, Atlas of the North American Indian, 1985)

The Plains Indians were wandering people scratching a living, half at farming, half at running after the buffalo. To them the horse meant power and freedom. Up through Apache and Comanche country it spread like wildfire ... north to the land of the Blackfoot ... Instead of foot-people living on the fringes of the prairies, the Plains Indians quickly became the finest riders in the world ... Farming was forgotten. On horseback they could carry all their belongings easily, and kill more buffalo than they had ever dreamed possible.

(Kenneth Ulyatt, The Time of the Indian, 1975)

James Green: Native peoples of the Americas; Oxford University Press, 1993, page 19