We pollute the air, water and land in many ways, and the more of us, the more pollution produced. If each of us cut our carbon footprint in half, for example (very unlikely, of course) and the population doubled, we would have accomplished nothing. And actually, we're increasing our footprint and increasing the number of people. We use both renewable resources (e.g. water, food) and non-renewable resources (e.g. oil) and the more people there are, the fewer resources are available. It's simple arithmetic: the more people, the less stuff per person. Lack of resources and simple overcrowding within a country cause it to become enviously interested in the resources of its neighbors – and wars often ensue. Hitler's expansion into Europe took place under the title: Lebensraum: living space. The German people did not have enough space in Germany and therefore took over neighboring countries. Overpopulation is a problem for both rich and poor countries. While poor countries tend to have higher birth and growth rates, rich countries use more resources and create more pollution per capita. Looking...