Particularly the part about the "premature withering" of civilizations remarkably similar to ours.
We can draft in all the immigrants we want ... doesn't change the fact that our legal system, in particular, has slanted the (hedonistic) playing field such that marriage and children are an impediment and something which neither men nor women are much interested in until middle age when they've lost their vitality and their family is destined to come ALWAYS second to the Career they put first.
We are in decline.
Additionally, given the extraordinary attention paid to "population control" by our government, it's strongarming and coercion of of the weak and it's infliction of inhuman practices on cultures not nearly so decadent or "Enlightened" as ours, it's possible these lines were also most prescient on Dawson's part:
If, however, questions of population should give rise to war in the future, there can be no doubt that it is nations with wide possessions and a dwindling population who will be most likely to provoke an attack.
But it is much more likely that the process will be a peaceful one. The peoples who allow the natural bases of society to be destroyed by the artificial conditions of the new urban civilization will gradually disappear and their place will be taken by those populations which live under simpler conditions and preserve the traditional forms of the family.