One of the most inapt historical analogies you will ever hear is that which compares illegal immigration to the United States to the “barbarian invasions” which were the most proximate cause of the fall of the Roman Empire. First, Mexican illegal immigrants are not barbarians: they are civilized. They come from a literate civilization. Rome had absorbed many settled, civilized people into its empire. The trouble with the Germans was that they were illiterate tribal nomads. Mexicans are not.
Second, by the time the western half of the Roman Empire succumbed, it had already been five centuries since Rome’s republican consistution had given way to a new system called the empire: Rome in its republican heyday had never had much to fear from the Germans in their northern forests. Rome had experienced many civil wars, dozens of succession crises, tyrannical and crazy emperors, multiple emperors, interregna, and so forth. America’s constitution and polity is far healthier than that.
Third, the peaceful migration of Germans as individuals and families, comparable to Mexican immigration today, had gone on for a long time without destroying the Empire. It is a rare half-truth, in an article by Timothy Birdnow that otherwise gets most of its facts wrong, that:
The Germanic invaders of Rome, who would eventually overrun the Empire and usher in the Dark Ages… did not come as warriors so much as peaceful immigrants — some legally, most not.
Concerning the legality I cannot comment: this is a subject I would like to know more about. My impression from a variety of sources is that the Roman Empire just didn’t have immigration laws in our sense: to prohibit peaceful migrants from crossing the empire’s frontiers is just not the sort of thing that it had ever occurred to anyone they might have a right to do. This particular bad idea is a modern invention. I highly doubt that the legal/illegal immigrant distinction could be applied to ancient Rome in anything but a highly anachronistic way. This may be the kind of questions historians could not answer with confidence; at any rate, I cannot. (The Romans did build Hadrian’s Wall but this is the exception that proves the rule: it was only one, particularly dangerous, border where it was built, the motives seem to have been mainly military, and Roman power often extended beyond it.)
But as to the point about warriors vs. peaceful immigrants, the Germans who came as peaceful immigrants strengthened Rome. Problems began only in 376 AD when the Romans allowed the Visigoths, as a united tribe, to settle along the Danube as refugees from the Huns, and even then only because Rome seems to have broken its promise to provide land and food for a people whom it hoped to use to defend the imperial borders. If Rome had kept its word to them, the Visigoths might well have done just that. At any rate, peaceful German migrants were never a problem. On the contrary, the last greater defender of Rome was one of them: Stilicho, son a Vandal father, whose impressive campaigns thwarted Alaric the Visigoth for many years, before Stilicho’s murder paved the way for Alaric’s sack of Rome in 410 AD. Wikipedia mentions Stilicho’s “mostly barbarian troops” in his campaigns against Alaric in Illyria, and that he scraped together “a coalition of Romans, Alans, and Huns to defeat Radagasius at Ticinum in 406.” Stilicho managed to fight as far away as Britain, yet Rome fell in AD 410. What happened? Well, not only was Stilicho himself murdered– and Rome had no comparable general– but “in the disturbances which followed the downfall and execution of Stilicho, the wives and children of barbarian foederati throughout Italy were slain by the local Romans.” Naturally, then, some of those barbarian soldiers joined Alaric, and Rome could offer hardly any resistance to Alaric. I’m not sure whether much is known about this “thoroughly co-ordinated coup d’état organized by Stilicho’s political opponents,” but one wonders, especially given this ethnic cleansing aspect… might it have been planned and carried out by nasty Roman nativists, the 5th-century counterparts of Tom Tancredo and Russell Pearce. In short, it looks like Rome fell because nativist know-nothings murdered a talented immigrant general and his immigrant troops, who were doing the jobs Romans wouldn’t do, namely, defend Rome.
However, I want to focus on something different. If we take the long view, were the barbarian invasions really such a catastrophe? Civilization sank for a while, but it rose again, and better than before: freer, stronger, more dynamic and creative. Rome had long since lost its republic and its republican virtue, the whole Mediterranean civilization had descended far from its glorious climax in the 5th century AD, by the time barbarians sacked Rome. Possibly it was being ameliorated by Christianity, and the Eastern Roman Empire (or Byzantine Empire) may give us some idea of how that could have played out, had the West not fallen. Byzantium never produced anything like the many-sided genius and glory that the West was to give birth too. Or consider the example of China, the “universal state” (Toynbee’s phrase) of a different civilization, which though occasionally conquered repeatedly reconstituted itself for two millennia — two millennia, by and large, of slow stagnation, at least compared to the swiftness and progress of the West. Maybe the barbarian invasions benefited Rome.
Why? Because they relieved Western society of something that was encumbering it. They lifted a great weight. They put an end to Big Government, for worse and for better. One might wish it done in a more gradualist way, an amelioration or mitigation rather than a disaster. A huge price was paid. But at any rate it was done. In its place arose feudalism, a new and more contractually-based mode of governance, and transient kingdoms, and a little later, thriving republics like Venice and Milan and Genoa and Florence and the Hanseatic cities in the North. And the Roman civilization was not lost, or not entirely: vulgar Latin persisted among the people, fissuring into the various Romance dialects that evolved and were later amalgamated into French and Spanish and Italian etc.; proper Latin persisted in the monasteries, then the universities, remaining the primary language of text until the invention of printing, and the norm in a gentleman’s education until the 20th century. Old texts were copied, recopied, glossed, commented on, made the starting point for new intellectual endeavors. There was likely a decline in population; there was certainly a falling-off, for a while, of literacy, but when it re-emerged, more interesting things were being written. Had a Roman of the 4th century been able to visit the Europe of the 18th, he would have been baffled, yet he would have seen all sorts of traces of his own culture persisting. In some places, the Roman law survived as the customary law of the people; elsewhere it was displaced by Germanic codes such as that which evolved into the English common law; throughout most of Europe it was later reimported. Slavery had disappeared, as had the murderous public games that had shamed Rome even at the height of its civilized splendor. The Roman republic, to which generations of Romans had sadly and impotently looked back during the imperial centuries, became the model for new nations. In short, the barbarian invasions were the beginning of a great rejuvenation.
So here’s the question: if the United States were to open its borders, could it get the rejuvenation, the renewed dynamism, the great uplift of the level of civilization, without a Dark Ages in between? And really, that seems not an unlikely outcome. Again, the Roman Empire could easily absorb peaceful migrants, as can the United States. The incoming Germans were happy to integrate, particularly when they came as individuals, like Stilicho’s father, but the truth is that even those who came in as invaders and seized Rome by conquest usually admired Rome and its traditions and sought to preserve them. Thus, Theodoric the Ostrogoth, who reigned in Italy as a Byzantine deputy, though he began to reign in 493 AD, almost a century after Alaric’s sack of Rome, preserved Roman law and customs and presented his Gothic nation as a new incarnation of the “Roman army.” If even military invaders, ruling Italy by force of arms, could be so captivated by the mystique of the Roman state to the extent of exerting themselves to preserve it long after the Romans themselves had become unwilling to fight for it, who can doubt that a still-vigorous Roman Empire could have enjoyed the loyalty of limitless numbers of peaceful German immigrants consenting to be subject to its laws. By the same token, it is blindness to the point of hallucination to doubt that immigrants to America are primarily willing and usually eager to accept American laws and customs, to endorse and participate in its political system, to be numbered as citizens, and to behave like Americans in exercising their rights and respecting those of others, seeking economic opportunity, etc. Indeed, it is typical for immigrants to be better Americans than the Americans themselves, starting more businesses, for example. Just as Stilicho was more Roman than the Romans. An America without open borders would become quite a different place in a generation or two, and an American of 2012 might see in the open-borders America of, say, 2090, quite a different country. But he would see in it far more of what is really valuable in America– more entrepreneurship, more charity, more loyalty to the limited-government ideals of the Constitution, more freedom– just as an astute ancient Roman brought to Europe would recognize in it the best of his own civilization, taken to a higher level.