With quite a few states offering petitions to secede from the union, the question arises as to how strong the states would be as individual nations. What if they all seceded and then declared war on each other? This hypothetical question generated some very involved scenarios at Quora. Here's just a short snippet:
First came a period of massive migration back to the homelands. Facing the newly invented discrimination that will be created many felt the need to go back to their own people. While the individual states retained all military assets they couldn't control the individuals who fight. A Texas Marine stationed in California, would not fight for California. A soldier in New York would not fight against their home in Virginia and a sailor in Houston would not fight against their home state of Florida. The warriors returned to their home states and the states had to re-consider that when they measured troop strength of their new nations. Ultimately, they measured troop strength by how much of the population would return home.
The story has the war playing out, with various states joining forces and defending their borders. If you're a Quora member, you can read the input of others as well. Link -via Jason Kottke
Assuming no alliances were formed, which is a big assumption, the final survivors would be Colorado, Alaska, and Pennsylvania but not for reasons you might think.
Colorado, stuck in the middle, would be mostly wiped out early on from all sides, except for a handful individualist mountain-folk survivalists hiding in the mountains.
Alaska, too far and too underpopulated to have been considered by any other state, will have pockets of survivors scattered all over.
Pennsylvania, like Colorado, will have been wiped out early on...except for a couple of Amish farms, whose inhabitants:
1) Weren't aware of any kind of war;
2) Quickly dominate the area, since they've been living in a post-apocalyptic setting for 200 years and are used to it.
-Saying that, and I'm not even from there, or close.