Dunbar’s number is 150, I believe. But that’s the limit for ““real”” people, with names and addresses and birthdays. The magic is, however, they don’t need to all be real: a nation is a tribe, and nations can hold millions. You just need a few real people that you take as a stand in for all the others, and then keep doing it untill it encompasses the whole of humanity.

I say “just”, it’s not like it’s that easy, but it’s doable.