The Second War for Armageddon was the first great invasion of that blighted world by Ghazghkull Mag Uruk Thraka, the prophet-warlord who would in time become the single most dangerous Ork in the entire galaxy. His WAAAGH! fell upon Armageddon with almost no warning, a greenskin tide of such sudden size and ferocity that the hive world's proud defences buckled and began to give way almost at once.
The orks descended in their millions upon the great industrial hives and the poisoned ash wastes that surrounded them, intent on drowning humanity beneath the sheer crushing weight of their numbers. The Astra Militarum and the planet's own teeming population were driven to the very brink of collapse, the war swiftly becoming a desperate, close-run defence of the towering hive cities themselves as the greenskins battered without pause at their walls.
Into this roaring crucible stepped Commissar Yarrick, whose iron will and absolute refusal to yield an inch made him the living symbol of Armageddon's defiance. He held crumbling lines together through sheer force of personality, turned headlong rout into stubborn defence, and became such a figure of dread to the deeply superstitious orks that they came in time to believe him quite literally unkillable. Where the old commissar stood in person, the line held firm; where he was absent, the greenskins surged forward once more.
Reinforcements and the bloody sacrifice of the defenders eventually broke the greenskin assault and drove Ghazghkull from the world, but the cunning warlord escaped the trap, vowing darkly to return one day and finish what he had begun. That terrible promise would in time be kept in full. The wider history of the world is chronicled in the account of Armageddon.