Eh, if a hypothetical civil war broke out again, the initial split would be coastal states versus interior states, but then each of those states would further splinter. It would really be an urban versus rural conflict. I can't imagine the likes of Bakersfield and Fresno sticking with San Francisco and LA. This okay for coastal cities but interior cities like Denver or Austin would be screwed.
The following is pure speculation:
It would be interesting as the rural areas would have the initial advantage as they have more guns, more people with military experience and supply the food, but the coastal states could isolate and cut off supplies, then overwhelm the rural areas as they can out produce them or buy machinery and supplies (through having money and access to shipping lanes). The cities could also lean on their population advantage over time (particularly among 18-40 year olds and the non-obese). So, much like the civil war in the 1860's, the cities would take an initial hit, but outlast and overwhelm the rural areas.
From an International Persepctive:
I'd imagine Russia would support the rural side as they want the US out of international politics to create a vacuum for themselves to fill, and the longer the war lasted the better for them. Europe would probably align with the cities, as would Canada and Mexico. I would guess China would side with the cities, as they need their consumers or face massive employment problems.