Sometimes I like to think that this was all planned.
In the period right after WW2 or maybe even before that, I don't doubt that some elites knew that there was an over population problem either currently at hand or soon to get worst. You have to understand that banking and finance was done differently back then. So the problem of limited money supply, increasing populations, and limited resources was real.
Nowadays its different. Money is no longer pegged to gold. America's gold is the dollar and it can print as much as it wants, use deflationary economic tactics by making it the world reserve currency. And in doing so, globalizes the world and makes the world more prosperous (also Americanizes the world).
Anyways the point of my speculation is that the economic and social aspect of it (depopulation) may or may not have been planned.
BUT if it were planned, boy can you imagine a bunch of geniuses, scientists, and psychics employed by the elites of Europe (either post WW2 or pre WW2), all planning this out:
"Here's what were gonna do folks. Were gonna make America the dominant global country. The world will be under America's jurisdiction essentially. The experiment shall be done in America first, then to other countries. Its native population must be controlled through a slow process that involves social and moral decline. The sole purpose of this is to gradually reduce its population. The media shall assist in the propaganda and social degradation of the people, but technology and engineering must also play a major role in reducing the unnecessary need for the masses of working men (breeding men) in a post industrialized society. Before, these unhappy excesses of young men were sent to wars to fight and die in the millions, but things must change. Social and moral decline, with the assistance of engineering and technology, and corruption of the world's human females, must happen. There may be some dysgenics going on due to the social and moral decline but there will also be a lot of eugenics going on through the liberation of women. Some men will be very dominant, and most men, won't be at all but as long as they are neutered and kept in check, things should go as planned. All in all, the end result of this should be gradual human population reduction."
