Here’s Why The 2016 Republican Presidential Primary Could Make History

— -- The 2016 Republican primary is on course to become the most crowded in modern presidential history.

The GOP now has 17 major contenders for the nomination -- former Virginia Gov. Jim Gilmore announced on Wednesday -- breaking the record previously held by the 16 candidates who sought the Democratic Party's presidential nomination in 1972.

Counting presidential contenders isn't an exact science, however. There are hundreds of candidates each election cycle that run for president. And the term "major" is, of course, subjective.

But it's clear that 2016 is shaping up to be a record-setting election cycle. To understand why, it's important to know a little history about the presidential nominating process.

According to Sidney Milkis, a professor of politics at the University of Virginia and the Miller Center, the 1948 Republican primary holds the record for the most candidates -- 15 -- vying for the presidential nomination before the modern primary system was established. (Ultimately, the GOP nomination went to New York Gov. Thomas Dewey who lost to Harry Truman).

But something happened in 1968 to change everything.

The chaos of the 1968 Democratic National Convention in Chicago spurred a restructuring of rules and regulations that made the selection process more democratic, opting for caucuses and primaries instead of concentrating power in party leaders.

This shift in selection helped break down some of the traditional barriers to entry for potential presidential contenders.

Bruce Schulman, the chair of the history department at Boston University, told ABC News that the 2016 cycle may be the "height of officially declared candidates." That's because we now have a campaign finance system that requires candidates to declare their candidacy, Schulman says.

While the formal declaration of candidacy helps explain the record-setting size of the 2016 GOP pool, there are a variety of other developments that make this year's race ripe for competition.

One of them, Milkis says, is the ability of corporations to finance political candidates following the Citizens United Supreme Court decision in 2010. Milkis said this turned campaign finance into a “wild west kind of frontier."

"If you have one donor," he added, "they can keep you in the game for the long run.”

The 2016 election also allows the Republican party to take advantage of a White House with no incumbent.

Jim Lengle, an associate professor of government at Georgetown University, told ABC News that “the party that controls the White House for two consecutive terms nearly always loses,” in the next election, “so anyone in the Republican party with presidential aspirations sees 2016 as a great opportunity to win,” provided history repeats itself.