In biology, there is an entire field dedicated to the letter K. It stands for carrying capacity. How many organisms an environment can support. It's similar to the law of diminishing returns. If it weren't for this pesky fact, one could grow the entire world's food supply in a single flower pot. But there's a catch. There is always a limiting factor. Some are basic items, like food, shelter, water. Others get more complicated. Territory, mates, interspecies rivalry, pollution.
Years ago when I studied biology, my instructor informed me that the consensus of the carrying capacity of the Earth was 12-20 billion (his opinion was 12 billion). When carrying capacity is reached, it is not a pretty site, be it humans or animals. It involves famine, violence, starvation, cannibalism. Though some animals are better suited for rebounding from carrying capacity than others (sardines vs grizzly bears).
Anyhow, I believe a large part of the chaotic nature we see in our modern day world can be explained by approaching this carrying capacity. As of right now, the limiting factors appear to be water, ideology, and territory. Though ideology for the time being may be the main limiting factor.
