What / or who are they: Delaware, Pennsylvania, New York, New Jersey
Why middle: These were the 4 of the 13 original colonies that were between the northern and southern colonies.
Religion: this is the sentence you really like to write. There were all sorts of religions present, but not one of them could dominate. These 4 colonies had Lutherans, Mennonites, Calvinists (mostly Dutch), and Presbyterians.
Commerce: mostly agriculture at the time, but not restricted to 1 crop as the south was. Had good ports and growing cities (New York, Philadelphia). I like to include the well respected intellectual hotbed of people there like Ben Franklin.