And if you'll notice, county by county, it's not that red/blue don't exist in the opposite state. They're just outnumbered. For instance, most of northern CA is Red. Some places in backwoods TX is still blue (because their great great granddaddy wouldn't have no carpetbaggers comin' round their place). There are, as weird as it may seem, some reds in MA. Probably, many many more mods in MA than that.
Blues congregate around Urban areas. I could go into motivations for voting blue, but that's some deep analysis that probably wouldn't be accepted anyway. I know why reds in suburban and rural areas are voting that way; they're moderately secure financially (even those who don't have a lot) but are DEEPLY concerned about the morals of the country. Every trip to the city gives them more reasons to vote against the way big cities vote. Sounds silly on the surface, but it's true. They don't want to value what those in the city value because, well, look at the problems the city has. They're opposite people with opposite realities.
The same was true in Roman times...
