US parties have usually aspired to be catch-all parties and were not necessarily united at the federal level. Before the modern era they tended to have regional biases and distinctive battlecries if not policies.

What seems to have happened is that parties in the House of Representatives were very disciplined and under strict leadership control from the 1860's to the revolt against Czar Cannon in 1911.

The effect of that was to reduce the control of the leaders elected by the whole caucus and disperse power to committee barons in office through seniority and effectively accountable to nobody. Democratic Party committee leaders tended to come from non-competitive southern districts.

By the 1940's conservative southern Democrats and conservative northern Republicans had worked out they could work together. This was the heyday of the "to get along, you've got to go along philosophy of Speaker Sam Rayburn. It worked both within parties and between parties.

Barry Goldwater and his kind of conservatism emerged as a response to the consensus between the southern Democrats and the me too Republicans. At first it was not too effective a challenge, but as strains grew in the Democratic party over civil rights Nixon's southern strategy brought the moderate conservatives together in one party. This provided a base for the economic conservatives, the religious radicals and the social conservatives to mount an ideological challenge to the liberal consensus of the northern Democrats and the (usually dominant in Congress) conservative coalition of the southern Democrats and the northern Republicans (which was not conservative enough for the people now considered to be US conservatives).