Why would controlling boston, new york, and philadelphia be an important goal for both sides in war?

I know that Boston is a main port of the American Economics, so they would want it for exporting and importing goods. I would assume that Philadelphia would have a related cause. 

Master planned communities outside of chicago. note: population density means people living in an area per square mile. chicago, an urban and highly populated area has a much more higher density than a desert, amish community, settlement, or nomadic region.