I demand a TL of this. If I wasn't busy I'd write it myself.
What would happen to the west if say, California breaks off along with the Upper-Mississippi? Who gets Colorado and Wyoming and such?
I think Pacific Republic (I think if California goes, Oregon goes with it) could have a legitimate claim to the entirety of Oregon Territory and maybe the western chunk of Nevada, but otherwise, it's kinda out of grasp (through desert and rough mountains with no railways). I think the Missouri Watershed (Montana et al) would go with the Upper Mississippi if river access is that important, and the remaining territories (Utah, New Mexico) would be divided up between California, whichever side Kansas goes with, and whichever side Texas goes with (the CSA formed, and then Texas joined. If New York, New Jersey, California, etc. go their own way, Texas might see fit to do the same).
Which leaves for the Union the Old Northwest, Pennsylvania, Upstate New York, New England, definitely. Here's the Maybes for the Union.
New Jersey--not sure how serious its secession movement was. Might go out alongside New York for economic reasons?
Virginia, Tennessee, North Carolina, Arkansas--if the Union completely comes to pieces before any Ft. Sumter incident, Lincoln will see the writing on the wall and not even bother to demand troops. They might stay with the Union, or go south.
West Virginia--if Virginia stays Union, it's a non-issue. Otherwise, counter-secession is a possibility.
I'm honestly unsure of how likely Upper Mississippi is, to be frank. By this point, the railways were a viable alternative to the Mississippi, so Chicago and (eventually) New York hold more promise than does New Orleans at this point.
Of course, this is a worst-case scenario for the Union. It assumes that New York's secession is the straw that breaks the camel's back, which is not certain.
