Well, for as cool as it would be to keep New Africa, it isn't a proper Haiti-esque situation. There are still a hundred thousand whites in New African territory, and with winter coming up, well there might be a food problem.
Similarly to the cultural impact of a beloved Catholic monarch, the rise and fall of New Africa could mean a lot for the development of the young Union, in either the positive or the negative. If, however far down the line, conditions don't improve for minorities, like the African Americans, the memory of New Africa could be the very base of African nationalism.
Depending on the reaction to New Africa's defeat, I see the possibility of the nation going down one of two, rather polar opposite, paths. Either way, the Carolinas and Georgia are going to be political non-entities for a time as they recover as, though they'd have their votes, they wouldn't have a lot of political weight behind them initially as in OTL, being gutted by the revolt. The federalists and centralizers may be able to accomplish a thing or two in that time, might even see one of those three switch camps if siding with the federalists means greater federal support for repairing the infrastructure of the state.
On one side of the coin, it may be a cause for a great reduction of slavery in this timeline. Not necessarily its death knell, but with a slave revolt having devastated three states, there will be considerably strong arguments to oppose its expansion into the territories. 'Lest we see the Union almost torn apart again.' Depending on how resilient and difficult it would be logistically to route the revolt out completely, there's possibility for negotiation between the two sides, securing some freedoms, possibly designating a state for African Americans in the West?
Such might be a stretch, but it's likely to be a much more popular idea than integration based on the time period, even if representation in Congress is a bit distasteful to the views of false superiority in those times. There's potential in it to create a more us vs. then mentality that could damage race relations later on, but so early in the time frame and the more than likely still distributed African American population, even with their own state, the interactions in the affairs of the country and shared political interests of those in identical geographical circumstances could see them and the rest of the area well integrated with each other by modernity, though it'd be a long road.
Alternatively, after the rebellion is defeated, the general feeling could be that of highly oppressive vengeance. It'd certainly be grim, and I doubt I need go into details with any person of today what the brutality of slavery could be even on good days. Such could lead of repeat revolts, and continued arguments against emancipation, using ridiculous arguments that their freedom would automatically equate with violence. Something like that, or any of the other sort of hogwash reasoned at the time to support the peculiar institution. That could end up going a number of ways.
I'm glad you like it, even for things that (while likely) are still uncertain. The USA will be a Constitutional monarchy, with the King's powers being fairly weak. I think the best descriptor would be a "crowned republic."
And the improved association with Catholics is without a doubt one of the big reasons why I'm leaning towards Lafayette. Imagine an America more willing to assimilate when imperial ambitions turn towards Latin America, and an America more willing to take more immigrants from South and Central Europe. It's a big cultural change that would be pretty interesting in my opinion.
I find the phrase 'Crowned Republic' to be quite intriguing. There is ample opportunity here to explore different and unique views on society that did not occur IOTL. I could easily see the modernity of this world bringing a whole new assortments of hypocrisies associated with the U.S., as well as a unique view of itself that could become a popular topic of debate.
That subject being the United States continuing to claim the title of the birthplace of modern republicanism, despite having a king. I picture we could see a First Prince/Emperor (I'm kinda digging First Prince as title, it's certainly unique and would add to the State's claim to not be a aristocratic state by any stretch) or prominent politician arguing how the American monarch is different than any other. Speeches like: "The monarch is not given the divine right to rule by god. No, he is raised in American soil, like the sturdy oak, bred among a people of freedom, not to rule a people but be raised by them, with only the intent to safeguard their democratic freedoms forever." Lots of clever, largely philosophical arguments (hopefully better phrased than me in a rapid stretch of brainstorming) that can ultimately be reduced to self-aggrandizement by cynics but would see endless debate and flame wars on forums such as these.
Monarchy and Republicanism, twisted together in such a unique matter, in the shape it takes on the American psyche and how the government operates. There's a excess of options one could take such a culture over two hundred and fifty so years of development. The mental image of a successful and long lasting First French Republic (or something like that) existing in modernity, grinding their teeth whenever the United States declares itself the first bastion of Republicanism is so beautiful to my imagination.
I concur with the sentiments on improved association with Catholics. I'd often imagined a timeline where Canada came into the ranks, and ended up staying (rather difficult, but not unattainable under certain conditions) with the Union having a similar effect. Doubtless a singular person instance such as this would be more effective (being groups of people are much easier to turn into nameless, colorless evils), though in that case I'd not wanted to sacrifice the full republican spirit of the State's enterprise (hadn't considered a different view than anything in OTL, the 'crowned republic').
Speaking of the Québécois a moment however, Lafayette's cultural impact will also assist relations with that group. Shared French descent won't do much because of the Québécois general resentment towards the French for abandoning them. Later generations after Lafayette would likely find love from the French Canadians in their shared respect for the French language. Even if the majority of the nation lies in other beds of culture and belief, having a figure at the helm that holds the traditions and practices of the minority in adoration would do a lot to assuage their position in the Union.... if it ever came to that haha
Really? I had not realized.
One unfortunate side effect of a Catholic monarch may be an association between hard line republicans and hardline Protestants in the years too come.
One notion bouncing in my head is that New Hampshire holds to republicanism and withdraws from the union and is joined by Vermont and Maine in a Northern Union.
My assumption is that the only way New Hampshire could do that is if a new, rebel government is declared. The representatives of the legitimate state government ratified the Constitution, in which a section of the agreement was a vote would decide whether the government would be purely Republican or a monarchy. In other words, they agreed to the authority of the vote's ruling when they ratified the Constitution. They would've likely suspected it would've fallen easily on the Republican side upon signature, but....
It's true , of course, that they could declare independence anyways, but it'd be for nought. Whatever men lead this cause, even if they were the ones who signed the document, would be declared illegitimate and a new state government would be declared. They could let them go, but that would mean secession is acceptable practice, a bad principle for a blossoming union to espouse.
I doubt Maine would find itself joined to them, as it is still legally part of Massachusetts. Inhabitants will be few, and far apart. Even if they side with secessionists, they're rebels against the state of Massachusetts. New Hampshire would probably spring right away from that rather than join, as it'd be a gainless engagement that would only obliterate the already dismal chance the Union will allow them independence.
And Vermont, well... the major problem with the independence of any of these three, regardless of the other reasons I've listed, is the most prominent one for why Vermont won't be allowed exit. Giving up any of these northern, underpopulated territories is essentially inviting the British to set up shop. They'll either dominate the small republic(s) in every aspect, or outright annex the lands into Canada. No one wants to feed the British anymore land, it'd be a nightmare for the American self-image if nothing else. Thirteen united colonies fought until freedom, only to have one be swept back into the fold, it'd be humiliating and rhetorically damaging.
Vermont's invasion could also be easily warranted by Congress and King. As of the revolution's end, New York and New Hampshire both claim the territory as their own. If it's solely Vermont, it could be split down the middle between the two. If New Hampshire is part of the fighting, New York will swallow it whole. It'd spell the end of an OTL state, at least for a few decades. No doubt separate statehood movements would be rampant around the Green Mountains either way, with a good chance of being successful once time dulls memory.
In all frankness, however, part of me would much enjoy some British intrusion on what should be American soil in these stressful times. Could alter the political climate in interesting ways, and bring out revanchist patriotic tendencies later on in time.
Also, ya, possible Catholic influence will definitely set those hardliners in the Republican camp for a time at least. Might discredit some of the more extremist views of the group in timeline, but the monarchy will already be severely limited by the democratic spirit that permeates through the country, so they likely won't be synonymous. Then again, it's unlikely anyone comfortable with the constitutional monarchy and its restricted king would self-affiliate as a Republican, rather likely a Democrat as the term becomes more accepted. The affiliation will likely change or wear off as time goes on and the political system evolves. The Democratic Party is no longer the bastion of conservatives and people of the Deep South after all.