Comment by ThunderSizzle

Massive immigration would cause the system to completely collapse as imported people will not respect the local economy, culture, etc. in the same as natural citizens that originally built the nation. That's not xenophobic, just reality. Importing people means importing their culture, which might be incompatible with the state.

It's a reason they began to be called nation-states - states without a nation backing it tended to flop, and nation's without a state tended to slowly (or quickly) be absorbed into the dominant culture.