The U.S. will fall for the same reasons as did the Romans, Athenians, and the ancient Egyptians. The manifestation of the coming collapse, however, will be somewhat different and more spectacular. When the U.S. collapses, it will drag down dozens of mature societies (western nations) with it. The U.S. might not even be the first ship to go under; the catalyst. Thus, this collapse will be global in nature. I expect that our modern lifestyle and standard of living will be destroyed, and the social welfare system will all but disappear (it will not be a good time to be old, young, or a single mom on food stamps). It is also likely that tens, if not hundreds of millions will die during the coming age of scarcity.