Iowa is the first state to vote for its Democratic and Republican presidential nominees by simple chance. It’s only been first since 1972, when Iowa officials planning the state convention had to reschedule the event on an earlier date because there were no hotel rooms available in Des Moines on the weekend in June they had selected.
Moving the state convention up meant moving the district conventions, county conventions, and caucus up as well, and thus the caucus ended up in January, ahead of New Hampshire’s primary. Very little time was spent campaigning in Iowa in 1972, but in 1976, Jimmy Carter invested time there and built momentum that helped him eventually win the White House.
Iowa has been guarding its privileged position ever since, and candidates compete fiercely for that momentum Carter tapped. If a state tries to move up its caucus or primary, Iowa moves its up even further. Iowa’s first vote is often criticized because it is a rural state that is very white: it doesn’t reflect the demographics or lifestyle of the country as a whole.