benji, tell us about the old primary system.
Candidates tended not to run, until the 1940s.
Many times stand-in favorite sons were used, this was how LBJ ran most of his bids.
Often, one or two states were seen as the deciders, generally New Hampshire, Wisconsin, Oregon and California were the states where anything "actual" happened. JFK poured his family and money into Wisconsin to show he could win as a Catholic, and knock Humphrey out of the race.
Some candidates created their candidacies out of the primaries, Harold Stassen, Hubert Humphrey, Estes Kefauver, Eugene McCarthy, Robert Kennedy, etc. all tried to use primary wins as "free media" and all of them lost the nomination because the primaries didn't dispense enough delegates. In 1968, Humphrey didn't win any of 14 primaries (got 2% of the vote) but most agree he would have won the nomination even had RFK lived as HHH had almost as many delegates as RFK and Eugene McCarthy combined. He won 1760-601-147-67-17-13. (HHH-McCarthy-McGovern-Phillips-Moore-Ted Kennedy.) McCarthy never had a chance because the Kennedy delegates refused to vote for him and that's how McGovern's presidential ambitions got turned into a career.
In 1952, only 12 states held GOP primaries. Eisenhower took five, Taft took five, Warren won his home state of California and Stassen his of Minnesota. Thomas Dewey and Henry Cabot Lodge claimed Taft had stolen the delegate slates of many states, so had the convention vote to get rid of the delegates and put Eisenhower delegates in their place, it won narrowly and Eisenhower relatively coasted to the nomination. Dewey then placed Nixon on the ticket.
14 states held Democratic primaries. Adlai Stevenson didn't win any or run in any. Estes Kefauver won 12 of them. Kefauver entered the convention with 340 out of 1230 delegates. Stevenson got 273 on the first ballot. Stevenson won on the third ballot 618-275-261. (Richard Russell third.) And to balance the northern progressive Stevenson picked a segregationist from Alabama for the VP slot.
1972 didn't see a full slate of primaries yet and was only contested really on the Democratic side. The lack of a full slate led to a huge disconnect between the popular vote % and delegate count:
Humphrey - 26% - 67
McGovern - 25% - 1729
Wallace - 24% - 382
Muskie - 12% - 25
Scoop Jackson - 3% - 525
Chisholm - 3% - 152
1976 are considered the first real primaries because it was the first cycle every state held a primary, it was contested in both parties AND it determined the outcome. (Carter won 30 states, Ford won 27-23. Both got the nomination, though there were enough undecided delegates elected that Reagan could have won at the convention. Carter went into the convention with a clear majority of elected delegates.)