Historically speaking passports and border controls have been the exception, not the rule.
The reason you can’t conceive of it possibly working is you’ve only ever lived in a world where you need a passport to go somewhere.
The scenario of 100 million people suddenly arriving is FUD. Apart from not being likely even on purely logistical grounds, the questions you’re asking are ones that are eminently answerable: Where do they live? In houses that they build. Where would their children go to school? At schools that they build and staff. It’s from the same fearmongering stable as “theytookerrrjaawwwbs”.
Historically speaking passports and border controls have been the exception, not the rule. The reason you can’t conceive of it possibly working is you’ve only ever lived in a world where you need a passport to go somewhere.
The scenario of 100 million people suddenly arriving is FUD. Apart from not being likely even on purely logistical grounds, the questions you’re asking are ones that are eminently answerable: Where do they live? In houses that they build. Where would their children go to school? At schools that they build and staff. It’s from the same fearmongering stable as “theytookerrrjaawwwbs”.