1) Ecomonic collapse (No supermarkets, no convince of modern life) - This will start it. Weakening of consumer power, walk down of middle/low class quality of life.
2) Martial Law (Government take over, concentration camps, King Trump) - with a weakened economy and a lack of resources, the way is paved for this.
3) Nuclear Fallout (Live in an radioactive wasteland, supermutants & deformed ppl) - Recognizing the weakening of the US and seized control by Government, other world powers attack with the intent on invasion and takeover.
4) Zombies (Reanimated or diseased/contagious people) - Waste from the fallout creates infected humans/Zombie-state.
5) Rapture (demons & shit) - Realizing that it's all about to fall down, the creator decides to start over. Sends the clean up crew.
^^^In my new book entitled 2024 A Trump New World (j/k)