I'd guess this would happen due to a failed Constitutional Convention.
Best case scenario you get two, maybe three confederations of states with similar interests, philosophies, ect. They would probably be centered around Virginia, Pennsylvania, and New York.
Worst case scenario, the states start fighting with each other, Britain swoops in and gobbles them all back up, favoring, of course, the states that sided with Britain, meaning Virginia and Mass. probably get the shaft.
A middle-ground might be that the states sign a treaty keeping them all from waging war on each other at least for a long enough time for some of them to hold off an eventual British onslaught. A few coalitions form up through extra treaties, peace agreements, trade agreements, ect. If war starts up again with Britain, it's hard to say what will happen.
Either way, this prevents any American territories from expanding beyond the Mississippi in all likelihood. New York will control Michigan and Wisconsin. Pennsylvania will control Ohio, Illinois, and Indiana. Virginia will control Kentucky (and West Virginia, but that wasn't a state until the Civil War, so...). North Carolina will control Tennessee. Georgia will control Alabama, Mississippi, and if it invades Florida, that too. The smaller states might find more creative ways to expand, not wanting to be gobbled up by their larger neighbors. New England will probably buddy up together to ensure this, and they might start "American colonies" in other parts of the continent under the banner of either New England or whichever state funds said colonization. New England would probably be one of the only areas with the funding to do this anyway. I can't say I know what will happen with Maryland, Delaware, and South Caculacka. History takes a lot of odd turns, so who knows.