Here are just some nations East of the Mississippi, in the current U.S, that could exist assuming a PoD of the Articles of Confederation falling apart. I also made a write-up, assuming it is 1900 at the time of this map:
New England (Pink): After the collapse of the Articles of Confederation, New England was very much like the Americans as a whole; weak, divided, and surrounded by land-hungry powers. For basic survival, the States banded together quickly, with a Capital in Boston and an interest in defending themselves both from British and fellow American encroaches. They sought to gain land in the West, especially as many of their States had claims there, but were thwarted by other expansionist powers as they had no land or sea connection to get there. Nevertheless, New England remained a huge hub of emigration West, as countless New Englanders set out to gain land of their own; this was mostly allowed by foreign powers as they posed no real threat of a takeover and helped fill up Western claims for countries. Back at home, New England became an industrial and commercial power, but were outstripped by New York as the 19th century drew to a close. Today, they are still economically relevant, in industry, fishing, and mercantile trades. Major cities like Boston and Hartford have seemingly been overrun with Irish immigrants, to the point that their national identity is almost as Irish as it is Puritan. They boast one of the most healthy democracies in North America, a Parliamentary System that is strongly centralized, but politics are sharply divided along ethnic lines, with Protestants and Catholics nearly at each other's throats. Meanwhile, New England's policy is heavily influenced by Britain, who they have turned to in an effort to stave off New York control.
New York (Cyan): Although blocked by geography from taking great tracts of land in the West, they did managed to take valuable portions and ensure that no one else could take those tracts of land. Pennsylvania and Virginia had originally moved into what is today Ohio, but soon found an Ohioan Independence movement (funded and supported by New York) ousting them to establish a farmer's Democracy. There was no such rising in Cleveland or the Erie Coast under New York control. Over the 19th century, the country incorporated a highly dependent New Jersey and skyrocketed past their Northern Neighbor to become possibly the strongest country native to North America. Their industrial power is massive, as is their control over commerce in North America. Their population is large and they have a great amount of influence over their neighbors. While they are officially a Republic, politics is dominated by political machines controlled by big business and political elites, with brutal repression of worker's movements (this has led to a rising Socialist movement). Their influence over their Western neighbor could be seen as slipping, however, as Ohio is starting to become a major power in its own right.
Pennsylvania(Red): Poor Pennsylvania. First New York made sure to occupy the Erie Triangle and points West, denying them a port in the Great Lakes, then Virginia nearly entirely blocked them out of Ohio with their own land, and then New York tore what lands had been gained in Ohio from Pittsburgh's grasp. Although no slouch, they were reduced to a bit player in North American politics, torn between the two titans of Virginia and New York. At first they were heavily influenced by the former, but now they are firmly a satellite of their Northern Neighbor, with many on both sides talking about annexation. Their political system would best be described as a troubled democracy, with the political machines of New York but with none of its efficiency, the rural populism of the West but with none of its success, and the Aristocratic attitudes of the South but with none of its power behind it. Although they host a fair amount of industry, almost all of it is owned by New Yorkers, and all of their goods end up in the Big Apple, one way or another.
Maryland(Purple): "Buffer State" would be the best way to describe this country. A former Slave nation like Virginia, with a very similar lifestyle to coastal Virginia. Maryland annexed Delaware early on with the consent of the latter, but had to give up the panhandle they controlled to Big Brother Virginia. Now they are a somewhat prosperous State with an uncertain future. It's not terrible to live there, but neither does the nation have much going for it. However, New York and its allies would never accept Virginian annexation, even if it was wanted, so there it will probably remain for the foreseeable future.
Virginia(Tiel): Virginia is a land of lofty ideals and Aristocratic tendencies. Perhaps the best of example of this is their first President, Thomas Jefferson, a man who despised slavery but yet owned dozens. In the end, it took 60 years after Jefferson had resigned to end slavery, and even still Blacks are locked in a sort of serfdom, commanded by their former and present masters in Sharecropping. Only when compared to Countries further south does Virginia's system of racial supremacy look good, which is according to New Yorkers just the way Richmond likes it. Even when looking past sharecropping, Virginia has a Republic built on the backs of poor farmers and ruled by ultra-wealthy elite. Indeed, their claims to a free Republic ring hollower by the day as laws recently passed allow plantation owner to essentially have their tenants vote for them, with repercussions for rebellion. Still, Virginia is still fairly well off, and even poorer whites don't do too badly. It is under-industrialized compared to states North, but especially in its Northwestern areas industry exists and thrives. Of all the places in North America, Virginia has the most civil freedoms of anywhere, provided they are for Whites.
The Dixie Confederacy/Slaver Confederacy(Shades of yellow/orange/brown): Not one country, but rather a pact between 5: Florida, Georgia, South Carolina, North Carolina, and Louisiane. The purpose? Defending against outside threats to the established order of slavery. Yes, in 1900. So why hasn't it been eliminated? Mostly politics. Sure, if Virginia, New York and New England could all work together, they could end the insidious practice once and for all. But that will probably never happen, and there's no way in hell anyone's letting British troops go any further South on the mainland than Canada. Britain's considered levying an embargo, but that would only strengthen Virginia, who they despise, and there's no way they could embargo Virginia as well, as that may finally be enough to get New York to side with Virginia. And that's without factoring in Europe....
And so the Confederacy remains, for now. However, Brazil just ended slavery, so Dixie is getting worried. Perhaps the Curious Institution is on the ropes, with falling cotton prices and international condemnation (though not action). But it's survived plenty of that int the past, so don't hold your breath.
South Carolina(Darker Green): The archetypal slave state. Never really got the opportunity to expand West, but had an elite who grew quite rich off of cotton. Prices decline now, but it still forms the basis of South Carolina's economy, as well as Dixie's in general. No democracy here: a King rules South Carolina, with various Aristocratic titles handed out to supporters, mostly for the prestige of it. Although they claim to be an enlightened monarchy, they hold countless slaves, and its not like the poor whites that aren't in on slavery are benefiting that much from the system. Sure, there's also a Parliament, but the King holds veto power and he and the aristocrats that support him completely control said Parliament.
Georgia(Yellow): King of South Carolina, meet the King of Georgia. They have a very similar system to South Carolina in general, though much more land in which to farm for Cotton and other useful goods to sell. Annexed West Florida in the 1820s, before outlaw Georgians took over Florida for themselves. Almost fought Louisiane for land, but circumstances found the Southern States banding together.
Louisiane(Baby Yellow): Here is another reason why slavery still exists: New Orleans. They control it, which means they control a lot of the trade in the Mississippi. Fortunately for nations upriver like Superior and Ohio, they let anyone trade, almost free of charge. But that could change if slavery was threatened. Louisiane never technically stopped being a French nation, with French elites in charge and some colonization from France coming in until the 1830s. But the vast majority of people who migrated here were from the rest of the South, and the nation quickly took on a Southern character. A cross-fertilization of languages and dialects has been discovered, with people speaking English like the rest of Dixie, people speaking French in New Orleans, and everything in between (including creole languages combining English and Creole languages). One thing they've kept from their French roots is their government: joint control between a Governor and commissaire-ordonnateur (or just Commissioner). One is chosen by Aristocratic families in a sort of Parliament, and the other is elected in a general vote. Sometimes these interests conflict, and the Governor tends to be far more Populist in nature. But everyone agrees slavery is good, as is control of the Mississippi.
Florida(Orange): The bastard child of the South. Originally a Spanish Colony, but with all the problems they had at the beginning of the 19th century, they didn't pay much attention to it. Georgian and other Southern settlers went into the state in a trickle then a flood, and though West Florida was annexed by Georgia earlier on, East Florida didn't remain a majority Southern State for very long. Many thought East Florida, too, would join Georgia, but things got complicated. The "Crackers" (as White Anglophone settlers in the area were called, at first derogatorily but later they would adopt it for themselves) didn't want to have much to do with their Elitist Georgian neighbors. It was actually a group of outlaws who started the Cracker revolt, as the Spanish Governor attempted to crack down on a bunch of robbers and highwaymen in the Northern part of the State. Perhaps this was intended to be a way of working with the Crackers by the Spanish government, but instead of gaining praise for attacking criminals, the criminals were turned into heroes and Crackers rose up against Spanish rule. After a few battles, the Spanish essentially gave up against overwhelming numbers and fled Florida. From then on, Florida would maintain a mean independent streak. This did not extend to slavery, however, which they vehemently defend.
North Carolina(Light Green): At first, North Carolina seemed to be heading on a trajectory similar to Virginia. They both extended West, picking up fertile lands in the Tennessee Valley and enriching themselves on cotton. They had a Republican system of government, and raked in cash from cotton. But somewhere in the mid-19th century, the two nations broke apart. Virginia grew bigger, adopted some industry, and eliminated slavery (at least on paper). North Carolina grew more steadfast in its support of the curious institution, refused to modernize, and generally turned in on itself. Today, life isn't all that different in parts of North Carolina and Virginia, but in other parts it may seem like the two are living on different planets. Norfolk, Cincinnati and Lexington are industrial cities not too different from those in the North, and North Carolina simply has nothing like it.
Ohio: The Ohio valley had always been a key region, since even before the Seven Year's War. It was no surprise, then, that Ohio became the region most fought over by the expanding countries of America. Virginia, New York, and Pennsylvania all staked competing claims to the region, with the first gaining the lion's share. This upset many of the Northern, anti-slavery settlers of Ohio, who despised the Southern Coastal Elite. Eventually fed up, they declared their own state practically out of thin air. It may have floundered early on if not for the influx of New York money, which guaranteed they could fight off Virginia as long as they left New York untouched. The militias of Ohio defeated the irregular army of Virginia, and set to work founding their own nation state. A conglomeration of Pennsylvanians, New Englanders, Southerners, and New Yorkers, they had to work to forge their own identity, and it developed into a cult of the frontiersman. Unlike the cramped confines of the Northeast or the Elitism of the South, they argued, here men could live free and forge their own destiny by owning their own strip of farm and defeating the wilderness. Their government became highly decentralized at first, only really existing for defense. However, as the 19th century started to draw to a close, it was becoming clear that this attitude was allowing the businessmen of New York and Britain to dominate the State's industry and resources for their own benefit. This was unacceptable to a state that was quickly becoming an industrial power of its own. Now rises the Populist Party. Opposed to big business and for the common people, or so they claim, they want to seize control of foreign-owned industry (especially railroads West) and give it to Ohioan businessman. Xenophobic and often antisemetic, when they seized power in 1897 they created large militas to enforce that, causing a Financial Panic in New York and leading to a recession the continent (and to a certain extent Europe) is still locked in. The Ohioan regime ignores this, however, and continues their nationalist policies, including restricting immigration and arming the country. Relations with New York, once a firm ally, have gone from bad to worse, and the idea of "Greater Ohio" is being revived- that is, seizing parts of the West still owned by Eastern States, namely Virginia and New York.
Superior: Superior can appreciate Ohio's struggle to survive. A combination of New Englanders and European (especially German and Scandinavian) immigrants arrived in the Western Great Lakes region intent on carving out a new life for themselves in peaceful colonization. There was just one problem; they land wasn't at all empty. Indians fleeing West from Ohio and other American Countries finally found themselves organizing just East of the Mississippi. They believed themselves to be far enough away from the Europeans to settle and form their own nation, led by their visionary leader Tecumseh. When new white people arrived, they were almost instantly in conflict, and would be for much of the 19th century. The British, hoping to gain the area for themselves, alternatively helped the natives and Superiorans. Conflict could go either way, but the Superiorans defeated the Indians in the bedroom and through immigration, growing exponentially as the Indians dwindled in size. By the 1850s, it was completely inevitable that Superior would be established, and yet they fought on, the Indians being chased North into worse and worse lands, until eventually they became a British protectorate in Northern lands unfit for farming. The Superiorans, meanwhile, established a Parliamentary Republic with influences from New England, Scandinavia, and Germany, creating a democratic system for themselves that would rival New England's. Separated from other countries by distances involved, joining an existing state was never really in the cards. In 1862 they reached an agreement with Ohio on a border; it would be the Illinois River, but Ohio would keep Chicago (had they refused, there would have been a war that Superior would almost certainly lose). Today, they are also experiencing Populist tendencies like Ohio, but of a much less nationalistic nature, with Prime Minister "Bob" LaFollete nationalizing railroads and defending worker's rights on several different issues. They are perhaps the most stable Republic in America, but this has only come after an extremely bloody past. Economically they are doing alright, growing at a rapid pace while less dependent on the rest of the world, but with nowhere near the economic power of the Countries on the East Coast.