Ugh, not this again. It would tear itself apart by the middle of the nineteenth century if it could survive to that point. Their government was- deliberately mind you- too weak to do a damn thing. It needed a supermajority of the states to agree and had no means of federal taxation. Add in the rise of abolition and the rich but fragile south would turn their guns on them.
That's true, but what I don't think gets talked about enough is what would've happened if Washington had succeeded and the rebels afterwards managed to put aside their differences long enough to work out a stronger republican constitution, like the ones we see in Greece or Australia today. I have no idea what that constitution would actually look like--this is all wild speculation here--but it could hypothetically work.
Now, the independent, stronger US certainly isn't going to want to stay in one spot forever, trapped on the Atlantic coast. After all, even during the Revolt Americans were moving west to settle Ohio. In the case of an independent US, I think it's pretty safe to say that an alliance with Britain is off the table in the early years--too much bad blood there. But I also doubt America's ability to mobilize a large enough army to conquer any of the British holdings in America that are left over (which we'll call "Laurentia" for simplicity's sake), which means America must say goodbye to the OTL province of Columbia, the Pudget Sound and Vancouver City. I predict the US would go south instead, probably with British backing, to put down the Mexican Empire--a real thorn in the Crown's side IOTL. We could get from this an American Tejas (an idea not very well explored IOTL, I must admit), and possibly even the Californias under the old Stars and Stripes or divided between them and the Brits.
Slavery's a whole other deal. While I'd love to see Abraham Lincoln (first Prime Minister of the Dominion of America IOTL) leading the nation through a civil war as he did in this timeline, the slavery deal is likely to flare up even sooner here, given the South's greater voice in the nation, something that was heavily offset IOTL by the northern territories of the Dominion. I'd say the 1850s is the point of no return for civil war, though the tail end of the '40s is my best guess. Britain would hopefully aid the US to put down the Southern rebellion by now (I'd say seventy years is long enough to forgive and forget, right?) and stop it from being drawn out
too long... Ooh! Great idea here--what if the civil war becomes the catalyst for an earlier Crimean War-type conflict? Russians invading from Alaska would be possible here, assuming Britain doesn't buy it as IOTL, and you could see a crippled Mexico siding with the Ruskies just to get back at the US...
There's a lot of potential here, just need to get past that first hurdle of getting rid of the AoC. Personally, I say we do that by saving Ben Franklin from his untimely demise in 1777 IOTL. If there's anyone who could get the United States of America on track to be at least
kinda sorta successful, it's him.