Maybe not politically correct, but aren't the problems of the world directly responsible to one issue? 

There are just too many people. World population has doubled since 1960, and will double again in 100 years. 

Agricultural scientists are searching for ways to increase harvests to feed this explosion, pushing other animals out. Automation has reduced the need for masses of laborers. Human caused climate change will reduce habitable land. Countries least able to support large populations will expand the most.

Europe is already full and getting swamped with refugees. In USA, caravans of migrants are heading north, all with dreams of living like Americans. 

A nice house on 1/3 acre, two cars, kids in college. Only thing is they arrive with nothing. No education, no skills, no resources at all. Just a lot of needs. What are we going to do with all these people?

 Just imagine a world with modern technology but half the population. A paradise. But like the man said, political poison even mentioning it.

 Butch Gordo