New Hampshire is not the Midwest, it is in the Northeast/New England. And that is the first primary election.
Iowa, which caucuses, was generally early, and decided to be first back in 1972. After the debacle of the 1968 Convention, the Democratic party decided to spread out and reorganize the primary schedule.
There is nothing carved in stone about the primaries or the caucus dates, other than New Hampshire and Iowa both passing state laws that they will always schedule to be first. A few elections ago, when other states tried to move up, Iowa and NH both were threatening to schedule in December.
IMHO, there should be a few Tuesdays between mid February and May in which a large number of states should hold primary elections.