AHC/PC: One nation covering all of North America

with a POD as far back as is necessary, have all of North America be part of one independent nation as of January 1, 2000.
 
here's a rough idea.
The American Revolution does not happen; British North America stays together as one unit. The British invest heavily in North America to fortify it in the decades afterwards, as part of "Fortress North America". A parliament of sorts for most of B.N.A is tasked with overseeing this, making for less resistance than would be present if London did it themselves.
The French Revolution does not occur; the King allies with the Third Estate, most of the First Estate, and parts of the Second Estate, and crushes a noble revolt.
Another war occurs in the 1810s between France, allied with Spain (which is unhappy with Britain's actions in North America), against the UK. The British repulse all attacks on BNA and eke out a win after six years of fighting.

The war further harms the foundations of all empires in North America (including the British one); the British take Louisiana. In the 1820s, all hell breaks loose, and the Spanish colonial empire in the Americas falls. The French lose Haiti. In the early 1830s, BNA follows, with some guy bent on Manifest Destiny taking control, after leading a narrowly successful revolt against British rule (with slavery being the issue undoing British rule). By the 1840s, the choas in BNA has settled, with it all under the umbrella of some vaguely British-aligned politician. Over the following decades, the United States of North America slowly expands, with it slowly gobbling Mexico and the Carribean.
 
So, the easiest way to do this would be with a bigger United States. Here's one possibility for how it takes the continent:

1812: Decisive victory in the war of 1812, takes much of Atlantic Canada
1848: Even more decisive victory in the Mexican-American war, takes northern Mexico and maybe the Yucatan
1854: Ostend manifesto is a thing, Cuba annexed from Spain
1866: 1866 Annexation bill takes the rest of Canada
1870: Annexation of the Dominican Republic
1898: Annexation of Dominica
1903: Annexation of the Panama Canal Zone

By 1914 you just have some of Central America, some of the Caribbean and Greenland left to take.
 
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