During the civil war the US population was about 30 million.  About 150 years later it is somewhere around 315 million and the US has probably about twice the land area, but much of the increase comes from western states that are sparsely populated and Alaska.  Any population that continues to grow exponentially will eventually crash when it eats itself out of a food supply or develops a disease that kills off large numbers.  I often wonder if we are headed towards that.  I know, it's Thanksgiving, but on a day when we reflect on food and housing it reminds me that neither is an infinite resource.  The world can only hold so many people; how long until something major comes along?