[GloomyBoots]

It’s impossible to solve with immigration. Even with an immigrant population that was completely willing and able to assimilate (unlike those in question), that process takes generations and requires a lack of ethnic ghettos and a high proportion of native and nativized people relative to immigrants. No honest person would say that we could solve Japan’s falling birthrate by rapidly and continually pumping it full of Europeans and expect it to remain recognizably Japanese.

But anyway population fluctuates. These things tend to work themselves out normally when your main goal is the good of the nation and not just inflating the GDP as quickly and recklessly as possible.

[0xcafefood]

Right. And in fact, immigration doesn't solve the issue for a very basic reason.

A system that says "The number of working-age people must be at least 5x the number of retirees" is literally demanding unending (super)exponential growth. It's fundamentally impossible on a finite world. It's going to break down at some point. The only question is whether that happens before or after filling the developed world up with immigrants from the undeveloped world.