I took this comment from a post on another site because I believe it represents what is going to happen.
“They are so foreign to us the things we embrace as virtue they despise as vice. Conversely, their virtues are poison. They are a parasitic drag on this country that we can no longer endure”
The country is not divided philosophically or culturally by geographic state boundaries. Therefore the split will not occur along existing known lines of demarcation. The biggest differences culturally in the US are created between urban and rural populations and this is where the break will occur. When rural states states break away from states controled by urban centers the rural portion of adjoining states will want to join with the productive rural states. This will leave NYC, PHIL, BALT, CHICAGO, DETRIOT and other similar cities on their own. The urban areas will be the focal point of the collapse due to uncontained civil unrest.