A constant theme of the American politics in recent years (the '00 decade), at all levels, is the great and apparently increasing polarization of the political spectrum. Politicians talk about "partisan politics", and if you look at the number of votes in Congress neatly divided on "party lines", as if mindless robots are casting the votes, not living human beings, you understand these are not empty words. Commentators and pundits have observed an increasing tendency of some neighborhoods to become "unicolor" politically, as if there's some selection mechanism pulling diverse people apart. Changes happen at the high levels of any of the three branches of government and then people talk about that saying how they need to "get their country back" or how they just have gotten it back, as if an invasion has happened at some point and some foreign or alien force has taken over or has been defeated. And finally the media, supposedly neutral, allegedly existing just to inform citizens about events, seems to be shifting towards more partisan positions.
It is perhaps easy to dismiss these things as being just "politics as usual" - and maybe that's the case, at least presently. But this is not a random universe and things tend to happen for a reason, and when you observe trends which are this large and deep and persistent, you are entitled to start looking for a cause. It is this way because something caused it, and trying to find an answer to the question "why?" often sends you off in directions which are as surprising initially as they are satisfying (from the point of view of knowledge) in the end.
The thesis which I am advancing here is that the seemingly deep division in modern American politics has come to pass because this is a scene with two main actors - the two major parties - whose positions have slowly changed over many decades until they have stumbled upon two great attractors in the field of human psychology, and now are stuck. It's essentially the supremacy of psychology over politics, certain features of the human mind acting as mooring posts far from each other, preventing not only any further drift, but also most attempts at bridging the gap.
Let's begin with looking at the way the human mind works, using the triune brain theory, Transactional Analysis, and related models - the clues we'll find there will make the explanation pretty obvious.