OK, let's recapitulate this scenario.
A comet strikes the Earth. The biggest piece lands in the North Atlantic producing giant tsunami's that do graet damage to the coastal area's of eastern North America and western Europe and less so to eastern South America and western Africa. About a dozen or so lesser fragments strike Europe and the eastern part of North America.
Great amounts of dust and dirt has been thrown up in the atmosphere. This spreads around the globe, accompanied by an unseasonal cold front and an equally unseasonal rain front, blocking out much of the sunlight. Only a small fraction (if that) of that year's crop survives.
This is bad, but civilization would survive, if this were all.
Which it is not.
The North Atlantic Conveyor a.k.a. The Gulf Stream has been interrrupted, which causes unaccustomed cold in Europe (and current thinking is that once turned 'off', the Conveyor takes anything from a century to a millenium to get back to what it was before).
The ocean's phytoplankton does not react at all well to prolonged darkness (as nuclear winter studies have shown) and after 3 months or so experiences a population crash, that than percolates up the food chain.
The world's climate gets colder and (because less evaporation due to cold equals less precipitation) dryer, reducing the amount of land suitable for growing crops.
The blanket of dust takes several more years to disappear, reducing the sunlight and thereby the size of the harvest from the remaining land suitable for growing crops.
This means that the majority of the world's population, and the majority of North America's population is doomed to die, no matter what.
Climate-wise the humid sub-tropics like southeastern North America would be the most favored places in this situation. it remains warm enough to grow crops, unlike Europe, Central Asia and a sizable chunk of the Mid-West, and reduced evaporation through cold equals out reduced precipitation. In contrast most of the Mediterranean would become a semi-arid steppe, Egypt's Nile and the rivers of West Asia would be low, India's monsoon would largely fail, bad droughts would strike Java, Mexico, Cuba, the Sahel, and less bad droughts most of the rest of the tropics.
(See for some idea of this:
http://members.cox.net/quaternary/
So compared to China southeastern North America has far fewer people claiming a share in the available food supply, because of a low population density, made still lower by the casualties from the tsunami's and impacts, a large proportion of land devoted to cash crops, that can be converted to food crops, and a minority which the popualtion is racist enough to sacrifice if need be.
So why should there not be State governments whith the ability to raise militia's, keep out the excess of the inevitable refugees from the north, expel/kill off non-WASPs, raise the Stars and Bars?
wkwillis said:
The majority of farmland was in the river bottoms in the south and west, and on the coast. On the river bottoms and the coast there was good soil, no rocks, easier to build roads (and railroads and steam boats) to transport it to markets.
The Appalachians, Florida, Bahama banks and Cuba stop the Tsunami's from damaging lands further west.
wkwillis said:
But if one of them hit at the confluence of the Ohio and the Mississipi, there would be godawful flooding while the water pooled upstream, and then godawful flooding when the water breached the dam and went downstream. The shore is the other location of good soil and that will be flooded by the tsunami.
That smacks of special pleading. How likely is one of them to hit THAT special location? Anyway the Ohio and the Mississipi are big rivers - a hole made by a comet fragment would merely make them a little deeper and a little broader. Big deal.
Zoomar: It's not that I'm especially fond of Americans.
