Yes, the premise is a little silly. As several have pointed out, the political divide in this country doesn't break down to state borders, it breaks down to that red-vs-blue distribution seen on the last election maps. And the vast, vast majority of Americans simply wish to be left alone anyway.
Or at least so I hope. I don't know how in the world we'd burn the potato fields in advance of an invading army. Suckers are impossible to keep lit.
It would be red states vs blue cities and the war would be over in a couple of weeks. And that is only because we would be busy drinking their beer and eating their food barbeque style.