I was thinking a little more about Pinker's argument in the post below. The North and Midwest were settled by English farmers, he says, the South and West by Scots-Irish herders. Sheep or cattle are much easier to steal than land, and that produces cultural differences. One view is suited to settled, agricultural, pacified societies, the other for frontier areas where state power is weaker.
It occurred to me this is another version of a much more ancient division - between the nomad and the farmer, which stretches back ten thousand years to the very beginning of agriculture. Nomad groups tend to be more warlike , and can sweep in from the steppe to dominant much larger and more culturally refined civilizations. The Mongols swept in to dominate China. The Huns, Vandals and Goths subdued Rome. The Arabs conquered Mesopotamia, Persia and Egypt. The Turks in their turn conquered Byzantium and (by extension) Northern India.
The division is explicitly there in American history - ranchers versus farmers. "The cowman and the farmer should be friends", goes the song in Oklahoma.
And it is a major theme in a famous Chicano novel set in 1940s New Mexicothat I read recently, Bless Me, Ultima. A young child has to choose between the open range cowboy influence of his father's family and the peasant roots of his mother's family.
They are two very different sensibilities with very deep roots. Red and Blue go back to the beginnings of modern society, perhaps.