The monkey wrench that threw the Malthus population predictions on their collective head was the legalization of abortion. Countries that legalized abortion saw a marked decrease in population increases from indigenous/main grouping births. The USA and Europe both have negative birthrates in their primary populations with almost all of their respective population growth being supplied via immigration (legal or otherwise) or high birth rates of newly imigrated populations who hav as of yet to embrace abortion as an option.
The first of the real issues with our ever increasing population are already showing themselves and have been for the past ten years or so. We already have fought three separate wars for control of the oil corridor (masked as something else of course). The economic collapse although caused solely by stupidity and over indulgent often times plain criminal means is not an animal onto itself and disconnected from everything else either.
Next main problem should be showing up in about ten years (give or take a little depending on usage) as the fresh H2O supply system is taxed beyond its ability to cope with the ever increasing demand for potable water.
Some cities like Singapore already recycle every bit of their drinking water from sewage.
De-desalination isn't being made affordable enough to keep pace or be worked in as a replacement for current systems either.
And as proven so many times in history...when the water supply dwindles, so will the food along with it.
After that it will be power supplies.