TheDude, this is an interesting thread. Although ' suggested purely as an entertaining thought exercise' , it is important to discuss on some level, as a loose generalization of what the USA faces today, and likely on into the near future.
Although I have not read the particular book you are reading now, I am fairly well read on this subject. Although from here on in all we can discuss here are loose generalizations and comparisons.
My understanding is that most of the 'fall' was gradual with the Empire becoming more Germanized over the centuries, with the
exception of the barbarian tribes you mentioned, who initially did not integrate well at all, and the Huns(who were not Germanic), who were there not to integrate at all!( modern parallels to be draw about your 'friends' south of the border).
Before we go on, I really want to state that we should be careful
to try not to cross the line from cogent dialogue into xenophobia and racism. There are I assume, a few individuals here on this forum that are from ancestry that we may be discussing, and just out of common courtesy we should be aware that our musing here may offend.
The kind of divisions between people likely will not form along river lines, or geographical area's, but more along lines of urban/rural settings. We see this now as a process that has been going on for decades, where new immigrants especially those from the south migrate to large urban areas. So too with the barbarians in Roman times. People go where the money is, and a living can be made.
Athough for one part of the US's southern border the Rio Grande river would provide a brrier(if properly manned) that the Romans tried to provide with their 'Limes'
Loki, you are right of course. South of the border, is where the new 'barbarians are massing. And you only win a prize if you can convince America that this is a real threat that is shattering and morphing it's culture. You win the grand prize if you can convince the powers that be to acknowledge this, and effectively stop it. Of course we know this will never happen. Without the converging crises of ecological collapse and peak oil, America is already an empire in steep decline(can be friendly debated on another thread if someone wishes)
Daculling, really good questions, and relevant to America today. I feel that early on in the Roman Empire, certain Emperors and their beaurocrats, and provincial governors who were 'in line' with official policy did try to restrict ethnic movement. This would have been done in the border provinces. Keep in mind though, that their borders were to a large extent militarized. In the interior provinces there was less of a need. Later on as barbarian peoples pressed far more firmly on this 'crustal defensive line'(the 'limes') it was realized that restriction, or even deflection of these migrations was unlikely to suceed to any great extent.
Coupled with this was a severe (and sometimes only local ) depopulation of the empire due to various reasons, but mainly to constant losses in the almost endless wars that plagued the later empire, coupled with some really nasty plagues that swept through at various times. So how is this relevant to America, and her declining empire? Similar, but not identical problems. We are seeing(I believe) the beginning of what may be a series of endless wars coming up. America's population is not being decimated by these wars, but since there is as yet no enforced draft, the effect is the same for this empires army. Oh, and as an interesting side note the US is starting to do what the Middle to Late Roman Empire army did...recruiting foreign nations into the amy to fight it's wars. The Romans were experts at this. It started out as hiring into the army individuals from Germanic and other tribes, and snowballed into hiring whole tribes then whole nations/peoples to fight, with a promise of citizenship after service. The US is doing the same today, with a promise of 'fast track' citizenship. people should be woried about this.
As to trying to dominate other peoples with their culture Daculling, the Romans were experts at this. Offering the 'Pax Romana' and ctizenship were standard operating procedure. So too with the US. Today is offered the 'Pax Americana', iPods, Big Mac's and slammed down Honda's etc. It's been done for decades, and except for a small percentage of the population no one is aware of it.
Katkinkate, I feel you are spot on when you mention the Asian migration tidal wave that is hitting North America's shores. It started shortly after WWII and has grown into quite a surge recently. The powers that be are aware of this and actively promote it. Most if not all Western nations that are highly indusrialized are experiencing a population shrikage or a best a net zero loss. If you are a consumer/capitalist driven nation your economy must continually grow or it with sputter, slow down, and eventually collapse. This is well known. Well known by the govt, well known by big business/multinational corporations(whose allegience is to no country, people, or Empire).
As for barbarian invasions, well, its happen, its here for those who take time from their lives to look up and ponder important matters.
I might suggest for those who are interested to obviously read Gibbon's Decline and Fall if you have not already. The parallels with the Roman Empire are there, they are just of a different scope and magnatude.
It gives one thought to ponder.
A.