Corvus Corax - Istvaan Compliance Action: One of the more notable campaigns carried out by Corax and his Raven Guard Legion during the Great Crusade was the Imperial Compliance of the Istvaan System, located in the northern reaches of the Ultima Segmentum, far beyond the established heartlands of the Imperium. Though cut off, scout vessels ranging ahead of Corax's 27th Expeditionary Fleet had found evidence that human life on Istvaan III had managed to maintain a largely cohesive industrialised society that had endured the millennia intact, making it a high priority for contact and absorption into the Imperium.A long-standing autochthonic culture was prevalent on Istvaan III, which included endemic local mysticism and religious practice. This, coupled with a history of independence, meant that once contacted by the forerunners of the Great Crusade, the Istvaanians had first demurred and then denied Compliance with the Imperial Truth. Given the strategic importance of gaining the life-sustaining and industrialised star system with its large human population for the Imperium, a priority was given to achieving the Compliance of the Istvaan System. The War Council had one caveat when issuing this order that precluded the use of overwhelming force in order to avoid excessive collateral damage that would spoil this valuable prize.The task of bringing the Istvaan System into Imperial Compliance fell to Corax and his Raven Guard Legion as the warriors of the XIXth Legion had a reputation for the use of surgical strikes and precision in such matters. The black-hulled Strike Cruisers and gunships of the Raven Guard attacked without warning, systematically destroying Istvaan III's military infrastructure and taking charge of its seats of governance. The military forces of the indigenous Istvaanians were professional soldiers who did not break easily, even when confronted with the might of Space Marines. There was some resistance, but the last elements of the aggressive faction were destroyed by the Raven Guard at the Redarth Valley on Istvaan III. An Istvaanian delegation formally surrendered before the Primarch Corax and the 800 companies of Raven Guard Space Marines that comprised his XIXth Legion.The Istvaanians kneeled before the sable-armoured conquerors as a defeated foe but were welcomed into the fold as men of the Imperium. Though they had waged war against one another, the Imperial Truth had prevailed and the Istvaanians had sworn to accept its teachings. By proving themselves men of wisdom and civilisation, they were deemed fitting partners for the many other worlds of the nascent Imperium. The Remembrancer Order had not yet been foisted upon the Space Marine Legions by the Council of Terra at this time, but a substantial civilian contingent was left behind to begin the integration of the Istvaanian population with the Imperial Truth. Vardus Praal was left behind as the world's Imperial Planetary Governor to command Istvaan III in the name of the Imperium, to ensure continued Compliance and manage the dismantling of the traditional religious structures that defined the planet's autochthonous society.The established capital located at the sprawling proto-hive of Khry Vanak -- Istvaan III's political and cultural capital ("Choral City" in translation) -- was chosen as the site of Imperial power. Unbeknownst to Corax and his Raven Guard, they would return fifteen standard years later to the Istvaan System, to the world of Istvaan V, to bring the rebel Horus to account.