I think what's important with determining the borders of balkanized US scenarios is the context. Usually people go with a scenario along the lines of the Articles of Confederation staying in place and ultimately leading to the dissolution of the US, but what happens next is important. For starters, what was the event that caused the states to disregard the articles? Was it a dispute over the Northwest Territory? Did two states go to war against each other? Did New England band together and secede? And speaking of which, you'd need to explain why certain states would federate with each other. There's certainly plausible explanations for why states would do that, and if you offer one you should be good, but assuming the event that causes the US to balkanize isn't an earlier Hartford Convention or something, in all likelihood no federations of states will exist upon the immediate dissolution of the Union. I've seen a number of TLs where a balkanized US just immediately has the "Southron Commonwealth" or the "Confederacy of New England States" form without any explanation, which is something that I certainly think detracts from balkanization scenarios.