Why are states so red and blue?

Steven Pinker looks at the evidence.

If this history is right, the American political divide may have arisen not so much from different conceptions of human nature as from differences in how best to tame it. The North and coasts are extensions of Europe and continued the government-driven civilizing process that had been gathering momentum since the Middle Ages. The South and West preserved the culture of honor that emerged in the anarchic territories of the growing country, tempered by their own civilizing forces of churches, families and temperance.

I looked at Pinker's excellent (and very long) last book here.