Here’s a history lesson that isn’t taught in schools anymore. At least it wasn’t in mine, and judging by the way people talk about how very impossible it is to stop invaders, it isn’t now either. Short highlight version:
The Helvetii were a Celtic tribe that lived in part of where Switzerland is now. They were getting pressured by Germanic tribes moving down from the north, so they decided, along with a few neighboring tribes, to migrate to live with some cousins on the west side of Gaul (France). The best route there went through a Roman province. Historians estimate there were between 100,000 and 300,000 of them, including perhaps 40,000 warriors. They may have burned their homes so they wouldn’t be tempted to turn back, though the evidence is sketchy on that.
Julius Caesar got there ahead of them and destroyed the bridge at Geneva to stop their passage. They tried to negotiate, claiming they were just passing through (“Gosh no, we won’t rape and pillage, we’re just taking a walk here.") Of course, a crowd that size can’t travel without eating and destroying everything in its path. Caesar played along with the negotiations long enough to fortify his position, then told them to piss off.
The Helvetii took a longer path around through some mountains and started pillaging Roman territory, as expected. Caesar showed up with 30,000 men and caught them in the middle of crossing a river. He wiped out one side, built a bridge to get his army across, treated the wounded, and then pursued the rest. If tribes didn’t immediately surrender and provide hostages, they were wiped out and the survivors taken as slaves.
It’s generally thought that Caesar defeated them more completely than necessary to improve his standing back at Rome. If so, it worked. The Romans wanted nothing to do with barbarian tribes coming any further south, and weren’t too particular about how they were treated. Caesar’s campaigns in Gaul kicked off his popularity, which grew until he was elected dictator for life. He became so popular that the elites of Rome began conspiring against him, eventually leading to his assassination.
Julius Caesar had no A-10 Warthogs. If a nation of 300 million people wants to keep out 5000, or 50,000, or 1,000,000 invaders, the question isn’t, “Is it possible?” The question is, “How best to do it?” What methods will best:
- stop the invasion
- prevent future invasions
- limit the risk to the nation’s troops and citizens
- limit unnecessary harm to the invaders
- expose any internal traitors who encouraged or funded the invasion
- reflect well on the leaders fighting the invasion
Those are all factors, more-or-less in order of importance, that have to be considered while choosing from a whole range of lethal and non-lethal options for stopping the invasion. But regardless of the answers, if the invasion isn’t stopped, it isn’t because it couldn’t be. It is because the people in charge chose not to.