Iowa's first-in-the-nation caucuses will take place, and they have not played this large of a role since 2004 or 2008, depending on who you ask. Why? Because both parties have a lot at stake.

For the Democrats, Sen. Bernie Sanders of Vermont could upset national frontrunner Hillary Clinton, which would make it the second time she has been beaten at the start of the campaign season, and send the race into disarray nine months before the national election. This would show that Clinton is not unbeatable, and it could give him the momentum needed to capture New Hampshire, a state in which he was already leading, and South Carolina.

For the Republicans, real estate mogul Donald Trump — their frontrunner — could be made legitimate if he comes out successful, putting him ahead of the Evangelical candidate — Sen. Ted Cruz of Texas. The Evangelical candidates won in 2008 and 2012. If Cruz comes out ahead, it could make him the party leader, and it would for sure take Trump off the mantle — a position he achieved because of his rhetoric and debate performances. If an establishment candidate finishes above third, it would give that faction a sense of life, and it would give that candidate a much needed boost.

What is a caucus, and why does Iowa have such a huge say in the selection process?

A caucus is when voters meet in locations across the state to decide which candidates to support. Caucuses are controlled by the state parties, not the state itself. (States control primaries, however.)

In Iowa, and other states with a caucus, voters will gather at large venues, such as community centers and gyms, up and down the state.

The Republicans caucus like primary voting, with a ballot.

The Democrats caucus in what many believe is a fascinating spectacle, which is what makes Iowa and its process so special. People will then gather in the corner that represents the candidate of their choosing. If candidates — or the uncommitted voters — do not meet the party's threshold, then the people in those groups need to join a different group.

The Democrats got to the caucus system via the McGovern-Fraser Commission, which was created after the 1968 election. They got to the modern caucus system the commission pushed for multiple demographics to be represented, and the new process had to be open. Their first caucus took place in 1972.

The Republicans followed suit and had their first caucus in 1980.

Iowa Democrats went first in 1972, so all of their party deadlines would be met. Iowa Republicans decided to move their caucus to January in 1976 after they saw how many spotlights the Democrats received. Both parties enjoyed the attention they received and the influence they had, so Iowa's first-in-the-nation status was put into law.

Producer Eli Goodstein created the video. News Editor Max Schwartz wrote the text story.

Reach Producer Eli Goodstein here; follow him on Twitter here.

Reach News Editor Max Schwartz here; follow him on Twitter here.