KillerT
As Swan Station says you have left pretty much all of the north centre and NW of the country up in the air. Are they free to be allocated anywhere or do you have plans/requirements for them?
Anyway, to have a go. Possibly a POD ~1800 with a more determined attack on Spanish territories, as Napoleon's allies. This sees Cuba and Florida seized then a better organised campaign takes Buenos Aires.
After Spain undergoes a revolt against French occupation relations with Britain improve but the Spanish rule in the Americas has been weakened and by the time Napoleon is defeated Spain, in desperate attempts to rescue it's mainland position, doesn't push for the return of the islands, which have been integrated into the British trading economy.
In the south Argentina becomes independent but a number of British settlers, mainly traders, relocate to the south with the main settlement being at Port Nelson [OTL Commodoro Rivadavia where they quickly become involved in small scale ranching and trading with the local Patagonian tribes.
British possession of Florida causes tension with the US. Britain, wanting to avoid another war, turns a blind eye to the crushing of the Indians of the NW. [Only way I could think of getting a British victory in the 1812 equivalent without gains there].
Even so war comes, both due to questions of impressing of seamen and also southern encroachment in Florida, war comes and is markedly more bitter with heavy fighting in the south where British forces hang on aided by Indians and freed slaves. With the northern gains secured New England is even more embittered about the war, especially as it's economy again suffers a heavy hit.
As a result, at the end it is a clear, although limited British victory. In the south Florida loses some of it's western lands but is largely secured and strongly populated by a mixture of Indians, many escaping persecution further north, and slaves who have escaped from nearby plantations. [In a number of cases with the help of British sweeps of Georgia]. In the north Canada takes all of Maine and northern bits of Vermont and New Hampshire and the rest of New England becomes an independent republic, having defeated an attempted US invasion with British aid. [Having the sections annexed under the name of Vermont as if we have the current Vermont and Maine annexed the border becomes pretty insane. The northern parts of each state, annexed to Canada goes by the name of Vermont].
This leaves a lot of tension between Britain and the US, which gets worsened by Britain's ending of slavery in the empire in 1928. [Slightly earlier than OTL due to the influence of the Florida blacks and the favour they won for their bravery in the war]. This antagonises the US as there is even less chance of slaves who escape to Florida getting back.
In the US the loss of the northern states gives the slave holding ones an advantage in the senate. The lack of two OTL states [Florida and the since the rump Mississippi and Alabama makes only one state] mitigates this a bit. Also the presence of Florida discourages plantations in the south so some owners seeks to push more slaves northwards. This is not enough to make gains north of the Ohio but does means that Kentucky, Missisouri and Kansas are more clearly won by the slavery factions.
It also encouraged expansion westward, leading to more open support of the Texan rebellion in the 1830's and an open war with Mexico in 1839-42. The US wins this after a bit of a struggle and annexes not only Texas but also the New Mexico-Arizona-California region, including the Californian peninsula.
Since all those areas are open to slavery this threatens to increase the grip of the pro-slave faction so the northern states are agitating for securing northern gains. They are also frustrated that southern domination prevents high tariffs being established. This means markedly less money for the government and less industrial development for the north which is unable to compete effectively with European industries.
One result of this is that the eastern praries are settled earlier, although this means much conflict with local Indians. By 1845 Iowa and Minnesota have been established as states, although there is some doubt that the latter actually means the population requirements.
Another is that the US has imposed fairly strict restraints on immigration from Europe while also continuing to display hostility to any from Canada and New England. This eases the pressure on land but further weakens economic development.
There are attempts to settle the Oregon area but this also faces competition from Canada, which is seeing fairly rapid development, partly due to higher investment but more so because of more settlers. Coupled with transport by sea since the buying out of the HBC in 1838 there is substantial settlement of Oregon by British and New England settlers.
Things comes to a head with the discovery of gold in California in 1844. This prompts a major influx into the region both from America but also from around the world. It further compounds the tension between slave and free factions as despite the region being reserved for slavery the vast majority of the new settlers oppose it. [Especially since many of the new miners oppose the slave mines being set up by some of the eastern groups seeking to monopolise as much of the gold production as possible].
The tensions result in the short 44-46 Pacific war. This is rather sporadic and disorderly as the US is itself deeply divided while Britain is distracted by the crisis in the eastern Med where Russia and Egypt in alliance are threatening to carve up the Ottoman empire. Coupled with the bloody war in Germany. As such it is only after the crisis is over in late 45 that Britain turns it's full attention to N America. [Basically, with the US the state it's in I need something to distract Britain. Possibly better to have the crisis turn up towards the end rather than the start of the war given the rather chaotic outcome. ]
The war sees another disaster for the US with rebellion in California and ultimately unrest in the north leading to the break away of the northern republic, which includes the states of Iowa, Illinois, Indiana, Ohio, Pennsylvania and Delaware and those to the north. Oregon is recognised as a Canadian protectorate and the northern western states [OTL Idaho, Wyoming, Montana, the Dakotas and Nebraska were neutralised. The rest was recognised as the rump US, now overwhelmingly slave dominated.
One effect of this war is to incite further efforts in Canada for integration with the founding of the Kingdom of Canada in 1853, although British Columbia and Oregon provinces do not formally join until 1858 when the trans-continental railway is completed.
The northern states, which for the moment call themselves the Federated States of America undergo a period of fairly steady economic development behind fairly hefty tariff walls. There is some tension with Canada and New England, but this fades fairly quickly. The main concern is with the US which still claims the region and leads to war scares in 1851 and 1854-55.
However after this point the main FSA concern with it's southern neighbour is with the growing refugee problem from the south. Initially this is a matter of poor whites unable to compete with slave operated plantations and other operations and they are generally welcomed initially as sources of cheap labour. However the deteriorating condition of the US accelerates drastically in the 1850's and 60's with growing guerilla conflicts. Many blacks, including armed groups infiltrating from Florida are fighting an increasingly vicious and successful war with the controlling whites and many of the latter flee the conflict.
Things come to a head in 1864-67 with open warfare between the white rulers and the blacks now coming out into open conflict. A series of brutal massacres raises tension further and since most are white on black prompts growing international condemnation. In 1866 & 67 clashes at sea occur as American ships, accusing British ships, often Florida owned and black run, of running arms and a series of violent exchanges occur. May 1867 sees the British dow.
The following two years sees heavy fighting as strong British intervention means the remaining white pro-slave forces are repeatedly defeated. However tension rises with the FSA which is showing signs of identifying with the US and opposition to the British support of the black forces. In 1668 they send two armies across the Ohio and tensions rise with forces on both sides of the FDA - Canadian border mobilised. Some clashes occur but finally, with mediation by the NEF, terms are agreed. Most of the southern parts of the region is under black/British control and the vast majority of the white population have fled. Further north, despite the efforts of generations of slave owners to establish slave based plantations and industries but they have never been that successful and the stress of the war caused further problems. Hence it is fairly easily agreed for a partition.
The states of Virginia, Kentucky, Missouri, Kansas, Tennessee, N Carolina and Maryland will be merged with the FDA, which will assume the former name of USA. Texas and neighbouring territories will become an independent state. Both will give up slavery and free all remaining black slaves, compensation being paid for the limited number of slaves in Texas. The other lands to the south will form a homeland for the freed blacks, known as the SC [Southern Confederation] This will be under British protection but not a part of the empire.
The southern US has much reconstruction to perform and also to merge the population there with the increasing numbers of settlers from the north. There is tension between the two communities but also a feeling of hostility towards both the SC and their British protectors.
In the SC destruction is even greater and the population, virtually all black and lacking much technical knowledge, have an even bigger task. However they have some very rich land and quickly get much investment from Britain. Their past history means however they are unwilling to accept a formal protectorate and despite a steady inflow of immigrates from the British Caribbean they set their own course.
Texas increasingly sees formal slavery replaced by the importing of indebted workers from Mexico to do most of the donkey work.
After ~60 years of fairly frequent conflict and much tension N America, now split into 7 states [Canada, USA, SC, California, Mexico, Texas and Florida - haven't decided what to do with Alaska but probably ends up as part of Canada]
The bulk of Latin America develops pretty much as OTL with the only exception being Patagonia where the British settlers, joined over time by others make a common cause with the local tribes and support the kingdom they eventually form when they seek to defend their lands against Argentinian and Chilean encroachment. This leads to the recognition of the Patagonian kingdom as a British protectorate in 1873.
Well that grew like topsy but I think I covered most of the points you asked for. Something of a Brit-wank but the only real way I can see of reducing the US in the way required and since there are gains for Canada and a British presence in Patagonia and predominantly Anglophone Caribbean it seemed the only way. Unhappy with the establishment of the SC but the only way I could really see getting a majority black state in the region.
Steve
So here's the baseline spiel:
North and S. America look nothing like they do today. We have instead
1 nation covering pretty much all of current Canada plus Vermont and Maine-we'll keep this as Canada. (Anglophone majority)
1 nation covering rest of New England (naturally enough this is New England)(Anglophone)
1 nation across the South (ok the CSA to keep various people happy)(Anglophone with African American majority population)
1 rump USA
1 nation of California, New Mexico and a few other territories-call this California, Pacific States of America-whatever you fancy.
1 Texas-pretty much as now-perhaps enlarge with some additional gained territories (minority and ruling group Anglophone, rest Spanish/native)
1 Carribean and Floridean nation of Florida, you can also include as many Carribean elements in the near vicinity (not as far as T&T though)(Anglophone with minor Spanish)
1 Hispaniola plus Carib states (one collective nation -West Indies and Hispaniolan Federation)(as Florida)
1 Mexican state (perhaps lost some of its territory to Greater Texas and/or California)(Mixed population as now, Spanish speaking)
Brazil and Northern Latin America are unchanged, Patagonia is settled far earlier by British settlers (pop mix of indiginous and Anglo descended)
So work out how its got there and what are they like, possible ramifications etc....