An insideous radioactive cloud came from space turning the Dead into Zombies. The Plague spread across the world leading to the ZOMBIE WARS. Then a leading Scientist (and founder of ZOMBCOM) discovered that if you shoot them in the brain, they die! Then the same genius Scientist developed the Collar. With out the Collar they are a raging killing machine, but put the collar on and hey presto two red lights come on and the Zombie is a docile servant.
So civilization is now under the totalitarian protection of ZOMBCOM who have fenced in every community to keep humanity safe from the Zombies that wander the wild lands....