Australia
Right good crack at it, mate.
The US is too powerful to give in to military attacks. Internal conflict already is and will continue to be the downfall of the United States. We live in an era of greed, extremism, blind faith and apathy. Greed continues to corrupt the foundations of our system from the inside out; corporations caring about nothing more than appeasing their shareholders that they don't think about the future, about what happens after they're gone. Extremism ranging from religious extremism to extremist feminism to political extremism, where people feel the NEED to force their beliefs onto others without question, without debate and being stubborn literally to the death. Blind faith is running more and more rampant among the citizens, ranging from conspiracy theorists to anti-vaxxers and general anti-science bullstuff, to people in general not valuing evidence over faith, valuing emotion over facts to the point where they will outright deny the obvious because it makes them feel bad. Then on top of that you have the majority, the apathists, the ones who know there's probably something screwy going on but they just don't bother doing anything about it because they don't care enough. Only a small few actually care enough about the issues to do something about it, and they're by far the minority. They've managed to keep things together so far but if things keep going the way they're going now, more and more are going to go towards apathy or the other categories and it's driving the nation further apart than it already is. It's eventually going to reach a boiling point, and it's not going to be a fun time. (did you really read all of that? nice. good. don't be an apathist, please.)
Same thing that destroyed the roman empire. Internal corruption, economic collapse and moral depravity. All 3 of which are growing problems right now.
