>>510001553 (OP)That is the thing: In a closed system (borders closed), it is more or less irrelevant how many people live in a country as long as it has enough manpower to defend itself from exterior threats. Looking at the geopolitical boundary conditions (nearly everything is bound together by various defense treaties) and still persisting technological edge ( + nuclear weapons making an actual total defeat very improbable) of white nations over potential outside threats, renders this point completely moot.
You have some smaller issues regarding average distances for centralized services like schools, hospitals etc. (less densely populated land) and simply not the absolute economic firepower to conduct any "Great Projects", but our current greatness-detesting ruling-class isn't interessted in pursuing anything worthwhile anyway so that doesn't matter either.
Without immigration to surpress wages, clog up any public services, siphon massive amounts of tax dollar and permanently increase land value, the birthrate would probably reach an equilibrium at some point. Given that the technologcial ramifications don't change that rapidly again (I don't think they will) and that the collective self-hatred and anti-natalism is eradicated.
As soon as you have massmigration into a democratic state, the whole system simply becomes a racial/ethnic headcount, which is why we either desperately need to increase our birthrate, simply kick them all out (easiest option and even mostly compatible with some nation's current laws) or institute an authoritarian goverment to manage our new multiethnic shithole (see Singapore for a rough idea).