The problems that we see now with over-population, resource shortages, wars, environmental degradation, water shortages, soil depletion, famine, etc. have been predicted by many leading thinkers since Malthus.  More recently these notions have strongly reinforced and the mass-migrations have been predicted by people such as Thomas Homer-Dixon and Jared Diamond.

It's too bad that nobody in positions of power listens to them.  The Four Horsemen are galloping our way as we dither...