> Imagine a scenario where a nation with billions of people under totalitarian regime sends millions of people to another nation. They instruct them to stay there long enough to become citizens of that nation. In the US that would be about two years.

Not how the US immigration works. For certain specific countries 2 years is a complete fantasy (perhaps for reasons you describe, no idea though).

I know people who lived here for over ten years waiting for a green card. These are people who went to school here, started families, have a steady job paying a ton in taxes, and yet are still nowhere close to being a citizen. Imagine having no real connection to any other country and still getting anxious every time you cross the border.