Well, it took me a while to think up of something that would cause a downfall and that is Global Warming. Yes, when it really starts to hit the planet it will raise temperature in impoverished countries that already have problems with the environmental/economic problems. The result of this will be that massive migrations will occur from nations such as Mexico, India and Nigeria. That in result will overwhelm the nations that they are migrating to and bring that country into chaos and lower the living standards in the host country. So in other words it seems that the people who don't believe in global warming are also the ones that want to close off the borders to illegal immigration... pretty ironic right?