Orks need battle just as humans need food and drink. Due to their warlike nature, they constantly fight amongst themselves, or launch piratical raids upon nearby enemies. Such conflicts tend to be small-scale or localised. They never really develop beyond random outbursts of violence and looting. However, Ork populations can reach a critical mass that leads to a full-scale planetary migration. This is known as a WAAAGH!, a crusade of pure aggression that crashes through star systems in an orgy of violence. An Ork WAAAGH! is war on an apocalyptic scale. Orks beyond counting swarm from one world to the next. Whole civilisations are exterminated and defenders' armies laid to waste as the Orks plough ever onward in an unstoppable tide.