The Roman Empire didn’t have a wall. Look at where they are today. Nowhere baby! The only important Rome any more is a line of ED products for men. Well, yes, the Vatican is there too.
There are also some great two-thousand year old ruins. Which brings me back to my original point. The Roman Empire didn’t have a wall. To be accurate, it did have a wall in what is now Great Britain to keep out the Picts (ancient peoples who were essentially the ancestors of the Scots) because they had tasted some of their haggis and didn’t want it messing up the superior British cuisine such as Bangers and Mash and Toad in the Hole. Scotch had not been invented yet, nor Irish whiskey, so these invaders didn’t have that going for them. They were a net zero when it came to bringing usable skills into the country, excepting the skill of pillage. This is a skill that consumers of large quantities of Scotch retain to this day.
You could say that the last 150 years or so of the Roman Empire project—until 476 A.D. when the Western Empire “fell,” was sort of an extended illegal alien immigration. Instead of caravans of ten thousand, there were caravan nations of hundreds of thousands. They crossed the frontiers into the empire, at first begging to be allowed to stay, but getting much more insistent as time went on. They were especially insistent that they didn’t want to be assimilated.
One of the dates that rings down the ages like the Clap of Doom is 376 A.D. when the Goths (no, not the teenagers who painted their faces white with dark eyebrows and lipstick to look like unhappy vampires—that is also two thousand years later but a Germanic tribe) requested asylum from the Huns and permission from Rome to enter the empire by crossing the Danube. You may have heard of the Huns. They were sort of the ISIS of the ancient world, except with a lethality multiplied by a factor of about a hundred. The Gothic dreamers wanted to come into the empire to get away from the Huns, and to bring all of their family members with them.
The Emperor Valens decided to go meet the Goths with about 50,000 ICE agents. That wasn’t nearly enough to process all of the Goths, many of whom claimed that they were fleeing persecution. The Roman Senate wouldn’t give the emperor the wall that he wanted to build along the Danube frontier and the Roman Supreme Court (Summi Curia Romana) ruled that the empire wasn’t allowed to halt the Goths at the river. They had to allow them into country to be processed to demonstrate that they were actually refugees. Actually, I made up part of that.
So suddenly the empire had a lot of excess labor that was able to undercut Roman citizens by underbidding them for jobs, or, when that didn’t work, to undercut them literally by chopping them up into little bits.
When Valens showed he ordered the Goths to disarm. They refused. Things got confused. Fighting broke out. And suddenly, like General Custer some 1,500 years later Emperor Valens was dead, and so was a large part of his army.
So, in a way, the Fall of the Roman Empire can be seen as failed immigration policies.
China, on the other hand, did build a wall. They did such a good job of it that you can see it from Space. It did not, however, keep the Huns out. What lessons can we draw from this? Beats the hell out of me!