There's already a split between the blue states on the coasts and "flyover country". This can only increase as industries move out of overtaxed, overregulated states and flow to where the new vitality is. New discoveries of raw materials and energy in red states like Texas and the Dakotas, combined with lower taxes and labor costs will drive a new recovery there, while an influx of illegals and inflexible "entitlement mentality" continue to depress the blue states. Obama is doing all he can to supress the new economies in the red states; they're waiting for him to leave rather than engage in open rebellion. If he wins another four years, they'll lose patience with him ( and the EPA, NLRB, Dept. of Energy, etc.) and force states to boot them out.
I don't know if it will be an actual shooting war, but I do know it'll take decades to sort out.
Look for intrastate conflict as well. California, Ohio, Virginia, Michigan, Illinois and Pennsylvania come to mind.
Look at a map of Ohio. Draw a line from Toledo in the northwest to Marietta in the southeast. In general, north and east of that line is leftist, south and west is conservative. We've battled in the state house that way for decades and I can see it getting worse as time passes. Here in Columbus, and even more so in Cincinnati, to be from Cleveland, Youngstown or Akron/Canton is often met with the same reaction as being from San Francisco or Detroit.