No one knows

Seriously! The Apocalypse came out of nowhere! As far as anyone (that's still alive at least) could recall, they just heard a sudden influx of car alarms, people's screams, things breaking, and then everything fell apart. Governments suddenly disappeared, money lost all value, and there was suddenly an infestation of crazy people that either looted or killed anything in sight. Now all the Humans that haven't gone crazy either lock themselves in their homes or pack up what they can take and try to find someplace that hasn't gone to hell.