In the 50s and 60s, there were really four parties, joined into two by coalitions. On the Democratic side, there was a social democratic, leftist faction, tensely allied with a Southern party (the Dixiecrats). On the Republican side, there was a pro-corporate but moderately liberal faction (the Rockefeller Republicans) allied with a harder-line conservative/liberatarian faction (the Goldwater Republicans).
Two things happened in the 60s and early 70s: the Goldwater faction largely took power in the Republican Party, and because the Democratic Party embraced civil rights, the Dixiecrats first flirted with independence (George Wallace's campaign) and then gradually switched parties, so now we have the oddity that there are people who fly Confederate flags but are registered members of the party of Lincoln. Many people who would have been Republicans in the old days are now the moderate/neoliberal faction in the Democratic Party.
So we still have four parties, they were just reshuffled. Now the tension in the Democratic Party is between the old FDR/LBJ new deal supporters, and their younger socialist allies, and the more pro-business neoliberals. On the Republican side it's between the business side (they don't care much about ideology, they just want to make money) and the hard-core conservatives.
Two things happened in the 60s and early 70s: the Goldwater faction largely took power in the Republican Party, and because the Democratic Party embraced civil rights, the Dixiecrats first flirted with independence (George Wallace's campaign) and then gradually switched parties, so now we have the oddity that there are people who fly Confederate flags but are registered members of the party of Lincoln. Many people who would have been Republicans in the old days are now the moderate/neoliberal faction in the Democratic Party.
So we still have four parties, they were just reshuffled. Now the tension in the Democratic Party is between the old FDR/LBJ new deal supporters, and their younger socialist allies, and the more pro-business neoliberals. On the Republican side it's between the business side (they don't care much about ideology, they just want to make money) and the hard-core conservatives.