American setting: the "crazy" thing was discovered in which country as the "starting point"
European setting: "Devil = Zombie" or the final army hidden by a mustached man after defeat is the "start" point
Japanese/Korean-style setting: either a strange "product" of some giant pharmaceutical company, or a mysterious substance leaked from a nearby biotech complex as the "starting point"
The Walking Dead-style setup: the spores from outer space are the "starting point"

Conclusion: Haha, the world has gone completely downhill. So, where is the safe zone.