This applies mostly to the United States, but to some extent it also applies here in Canada. But it seems that politics is the new divider instead of race. And the polarization seems to be getting worse. I noticed it living down there many years ago, and there is no sign of it subsiding.
So what gives? A book I came upon many years by David Hackett Fischer, Albion's Seed apparently holds the answer. The English Civil War was one between an upper class Royalists with certain views of the world and the emerging peasantry/merchant middle class with another set of views. When they migrated to the new world, they settled in distinct places. The puritans in New England and the Royalists in the South. The rest is history. It explains the US Civil War, the blue-red state divide etc.
This leads to the modern days culture divides. Clark of Popehat has the update on Albion's Seed.