In the aftermath of Judgment Day, we fled to the Exclusion Zone and sought refuge underground. This is what is left of our fallen civilization.

The Stockton Slap: Why Slapping Is the New Punching by Jack Slack
http://fightland.vice.com/blog/the-stockton-slap-why-slapping-is-the-new-punching

Little did they know that the Stockton Slap would become one of the 36 hidden techniques of the Wu Warriors, that allowed them to escape and form the beginnings of the Resistance.