Prior to the 1830s, a party's presidential nominee was decided through the – system. this was replaced by the national convention system, in which choices about who would attend the national convention were made at the – party level. later, in the twentieth century, – elections were adopted to introduce greater popular selection of presidential candidates.

Caucus system ... state party level ... primary elections.

In the old caucus system, the Congressional members of each party met to decide on who they'd put forward as presidential candidates.  There was no direct public input into the process.  Opponents of this sort of process called it "King Caucus" because of how undemocratic it seemed.

Even the process of state and then national conventions tended toward undemocratic influence, as party bosses tended to control who served as delegates at those conventions.

The use of presidential primaries took some time to become standard.  Today candidates are still formally chosen at the parties' national conventions, but delegates at the conventions are essentially ratifying the choices of local primaries and caucuses.