Yes, as both Koreas claim the other state entirely it's basically one country with two governments. I really should have put Taiwan in with China for the Cs, but most people accept it as a separate nation.
28K isn't enough to start a country with a proportion willing to wander off. That and they got hit really bad in the initial fighting after the event. Most survivors were wounded to some level and so in no shape to colonise new lands.
Geez, I get all the tl;dr for you to read
After 1865 why wouldn't it be inevitable, more or less? Perhaps not guaranteed, but after the defeat of the CSA the US stood as a totally uncontested power in all the Americas that could, at will, summon the largest army and navy on Earth (even if not the best trained). It had a continent's worth of resources that was virtually untapped, high population growth rate, was on good terms with the major powers of the day (there's a reason the UK wouldn't back the CSA in OTL), and a massive industrialized economy that was a rival to the British and, later, the German Empire. There's no real reason that the US wouldn't become at least a major power if not superpower because nothing could really threaten it. The only power with the naval reach was a friend who the US allied consistently with to this day (UK) and everyone else couldn't realistically touch actual American soil. Before 1865, maybe it'd be different, but post-1865 there is no real reason the US wouldn't be a domestically peaceful (compared to everyone else) world player outside some sort of self-inflicted idiocy like attacking the British or another civil war, neither of which came even close to happening IOTL.
True enough, but the US was also an extremely dysfunctional state socially. The south was an economic mess with a huge unrepresented underclass living in many cases in virtual slavery, the industrial north had ethno-religious tensions, significant corruption and was a mess of bad working conditions plaguing a highly dissatisfied urban working class, the prairie had problems with underdevelopment, isolation, and poverty, and the coastal west had simmering ethnic tensions like the east. I see in the First World War era US the potential for major problems if an event or series of events occurred in the right ways to set it off. In this case, economic collapse brought on by chaos in Latin America and general disruption of world trade following the dysfunctional partial end of war in Europe and the rise of Communism throughout the world following collapse of colonial regimes. That the US was actually losing the war in Mexico right while the economy went through the basement and socialist sympathy was high resulted in the conditions for insurrection in the northern cities and total social rupture of the twisted south. Essentially, the colonial-by-any-other-name stranglehold the US had on Latin America blew up in its face like the colonial regimes of the European states had.
So is much of Nevada.
(Seriously, in The Future it's the coastal regions of the middle east that are going to be screwed habitability-wise, not so much the interior). http://www.climatecentral.org/news/middle-east-future-heat-humidity-19599
)I imagine those that remained would be able to be subsumed into the population easilly enough. Plenty of Christians and, even if Korea is homogenous, there are still millions of women around. Bound to be a few thousand who would marry physically fit soldiers who would probably be getting paid by the Korean government for their services. Even if by using whatever the American government or businesses left there.
