Storm of Iron (Warhammer 40,000)

Ten thousand years ago, the Imperium of mankind was riven by a great schism. The Warmaster Horus, tainted by the corrupting powers of the warp, turned against the Emperor, and attempted to wrest control of the entire galaxy using Space Marines who he had persuaded of the righteousness of his cause.

Although foul Horus was eventually defeated, his legions of Traitor Marines continue to fight in his name, serving the Chaos Powers. Now a new Warmaster has arisen, with plans to bring all of the galaxy under the dominion of his undying masters, and the corrupted ranks of the Iron Warriors are readying for battle.