Entertaining this idea always intrigues me. There are few ways I can (somewhat realistically) see this happening... 1. America is in too much debt to too many countries and they come to collect...collapse of the dollar 2. Overwhelming terrorist strikes and invasion on the homeland (this country is full of foreigners from around the world) 3. Another recession that turns into a major depression 4. A series of natural catastrophes ....don't worry, I won't mention the zombie apocalypse. What situation, if any, do you see causing major catastrophe/collapse in the US?