Of course it's a possibility. There's evidence in history that there have been multiple cataclysmic events, such as asteroids, giant volcanic explosions, etc. We certainly wouldn't be immune. Some geologists even have evidence that practically all of Yellowstone is a giant supervolcano (check it out sometimes. It's kinda scary.) And anthropologists are always talking about the tendency of great societies to rise and fall. Societies form, grow, enjoy a period of wealth, begin to focus too much on frivolities (beauty, etc.), then fail. Rome anyone? I think nature is more likely to do us in than another nation, though.
On a side note, PPlaya123, farming is not a step back. Farming is still very much a part of American society and the American economy. If we didn't produce much of our own food, we'd be in trouble. For example, for anyone who's noticed the big jump in peanut butter prices recently, this is due to the extreme weather we as a nation have been experiencing which has effected the peanut crops, such as the drought conditions in Texas. Imagine how much more it would cost if we had the buy all of our food from other countries.