Note that until recently, there was little correlation between the progressive/conservative axis and the Democratic/Republican axis. The passage of the Civil Ri

Note that until recently, there was little correlation between the progressive/conservative axis and the Democratic/Republican axis. The passage of the Civil Rights Act of 1964 and the Voting Rights Act of 1965 led to the downfall of the Dixiecrat faction of the Democratic party and the current ideological sort. Ezra Klein's book "Why We're Polarized" has a lot of good background on this.