Alone among the majors, the U.S. is on a pro-growth population trend—not only because we have higher lifetime fertility rates than Europe, Japan, China, etc., but also because of our sympathy for immigration; we bitch about it, but we keep the doors pretty widely open. The odds are that by the end of this century the U.S. will be the world's most populous and prosperous nation. It will have about twice the number of people it has now; at least 500 million. By then India and China's populations may have crashed to only about 400 million each.
Let me see if I can wade through this open sewer of an idea.
We will be the most prosporous nation, after taking in over 60% of our population from the world's most backward nations. The immigrants bring nothing but active gonads, and hands out for a hand-out, yet the small, productive portion of the USA will be able to feed, not only themselves, but everyone else?
What keeps the USA on a growth path, but India and China lose 2/3 of their population?
Picture the entire USA as a Los Angeles and NYC on steroids. Kinda makes you want to disembowel yourself, doesn't it?
This post is speculation and it is Reaganesque in it's optimism.