And the USA is in that group now. We have about 1.78 births per women in the us and that number is declining. You need a birth rate of over 2 per women in order to sustain a population without immigration. If a place does not sustain their population their economy cannot grow and if your birth rate is lower than 2 immigration is the only viable option to sustain it. Less people = less specialized jobs = less overall jobs = worse economy.