Armageddon was settled during the late period of human expansion during the Dark Age of Technology around M20. There is almost no data regarding early human settlement of the world, all we know is that at some point during its history, heavy industrial expansion led to the population consolidating into ever growing hive cities and the environment reaching a tipping point and falling into an irreversible corrosive atmosphere. Clean air and water is a precious commodity on Armageddon, with most water being supplied by the southern continent, the Deadlands, being shipped by pipeline to the Hive Cities, as well as being imported from off world. Food as well is imported, as the massive population cannot be support by what meager foodstuffs are produced on Armageddon. The northern continent, the Fire Wastes, is where the majority of raw material is mined for production of war materials. The rest of the planet is dominated by industrially polluted ash wastes that are inimical to human life.
To be a man on Armageddon is to be one among untold billions, toiling away in the Emperors work to keep the alien menace at bay and ensure the Imperium has what it needs to fight its wars. Violence is endemic on Armageddon, as with many hive worlds. Many find the arms of the underhive gangs open, as long as they are willing to pledge their lives to the gangs. Those that do find a meager escape that the weak fall to in drugs and petty crime. Because of the sheer size of these gangs and the widespread conflict between them, the Arbites are hard pressed to crush them and instead seek to control the violence by punishing those that interfere with the needed industry of Armageddon, the rest left to slaughter each other as manpower is never an issue on Armageddon.
What makes Armageddon such an important world to the Imperium of man, the reason the Imperium supports this world with food and needed material for human life ot continue on this desolate world, is that it is one of the largest production sites of Chimeras for use by the Imperial Guard. As such, Armageddon's Imperial Guard and PDF regiments, known as the Steel Legion, are heavily equipped with Chimeras and other Heavy Vehicles and are known for their expertise in armored and mechanized warfare. Individual guardsmen all are equipped with hostile environment gear and can fight effectively in the harshest and most corrosive combat conditions and worlds.
The early history of Armageddon in the Imperium of man is relatively uneventful, as such things can be in these times. Reunited with humanity during the Great Crusade, M31, there are no records indicating the response of the population of being integrated into the Imperium. All we know that most conflicts regarding Armageddon during the early Imperium are minor and mostly involve the supply of war material and the regiments of Steel Legion to prosecute those wars.
Even in these early years though, the fighting skill of the Steel Legions was put to the test and not to be found wanting. The brutal struggle for life and the violence of the hive gangs has bred a natural skill for combat into the souls of Armageddon, especially in their favored form of war. Living all their lives in cramped spaces and a corrosive environment, the conscripted ranks of the Steel Legion need little training on how to survive in the most hostile of warzones. As such, their equipment reflects this fact of life. Their weapons are designed for close quarters and usefulness in the cramped environs of Chimeras and their rebreathers and uniforms are capable of withstanding the most corrosive chemicals.
The system of Armageddon is itself harsh, with only a few worlds capable of supporting life. Beyond Armageddon, there is Chosin. It is an ice world and extremely harsh, added to the fact that it is overrun with the foul Xenos Orks, managing to survive in its climate and launch raids against Imperial forces in the system. At this time they are contained but no eradication campaign has yet to be conducted to cleanse the xenos taint. The next world of St Jowen's Dock is dedicated to the Imperial Navy and is both a production ground as well as mobilization point for the Imperial Navy to conduct operations in the subsector, including the Armageddon system. The next few worlds are uninhabitable gas giants and are only exploited for the raw materials they provide, though no permanent presence is established. Pelucidar is a jungle world and is currently uninhabited, it is of little use to the production of war material that Armageddon produces and as such is untamed. The outer most world is Mannheim and its sole purpose is that of a monitoring station and outer defense of the Armageddon system, acting as an early warning for the Imperial Navy and Steel Legions on Armageddon.
Through the long history of Armageddon and it's system, the ork has been the greatest threat it has continually faced. Many of its worlds have endemic populations of the foul xenos that prove nearly impossible to fully eradicate. Because of this, the regiments of Steel Legion and even the citizens themselves have become accustomed to fighting them and many warzones call for the skills of the Steel Legion. Their hatred of the ork can only be matched by a few in the imperium, with Valhalla being one of the few who can claim to have such holy hate against these creatures.
While the Steel Legion cannot claim to have to military society of Cadia, nor the constant fight for survival of Catachan, to hone its people into soldiers, the constant battle against the each other and ork threats have proved more than enough to create some of the finest regiments in the Imperial Guard. To make to the point of being inducted into the Steel Legion means that one has survived a lifetime of gang violence and caustic environment, enough to hone them into the warriors the Emperor needs.
Because Armageddon produces so many Chimeras, its regiments have extensive access to them and they are famed for their mechanized infantry formations. The Chimera is to the Legionnaire what the horse was to the ancient Terran knight of myth and legend. It keeps soldiers of the steel Legion alive in the most hostile environment and carries into holy battle against the Emperor's foes. The Steel Legion is unlike many regiments of the Imperial Guard and excels at rapid warfare, blitzing their enemies and overwhelming them in a tide of steel and flesh. Their Chimera's advance into enemy lines without warning and disgorge their Legionnaires into the heart of the enemy before they can respond to the brutal tactics employed.
Due to the massive population and access of war material, the Steel Legion pays little heed to the lives in it's regiments. The losses taken are seen as necessary to do the Emperor's work and each soldier is willing to make the sacrifice needed for his world and Emperor. Those lost are replaced and the Steel Legion grinds on, winning the Imperium's wars no matter the cost, marking them as one of the most dedicated and disciplined Guardsmen to be counted upon.
It is in the end of the 41st millennium that the greatest fame and deeds of the Steel Legion been done. The first of the so called wars for Armageddon is shrouded in secrecy. Though few can pierce the veil cast by the holy Inquisition, there remains some information to recount that tale. Beginning around 400M41, a massive space hulk entered the Armageddon System. The following accounts tell of an unspeakable tide of Daemons, threatening to swallow up the whole of Armageddon. Through denizens of the warp and traitor cultists, the Steel Legion stood firm and fought in defense of their world until support could come. And it came, with the Space Wolves led by Logan Grimnar and mysterious marines clad in silver armor, their markings unknown to the the defenders of Armageddon. The daemonic hordes had wasted time building monuments to their conquest, and when they emerged from the equatorial jungle, they found the Steel Legion and Space Wolves ready for them, holding the Chaos taint in check. With an assault led by the silver marines, the heart of the Daeomic horde was cut out and sent back to the Warp. The ensuing months saw the eradication of those cults that had bartered their souls to the Archenemy. What followed though is not confirmed, but there are whispers that the remaining population of Armageddon was culled to prevent further taint. What is known is that at the end of the war, an enmity existed between the Sons of Russ and the Holy Inquisition, which lasts to this day.
While the nightmares of the first war are left to superstition and whispers, it is the second war for Armageddon that would thrust it into the forefront of the Imperium's warzones. The second invasion did not come from the Archenemy, but from the hated Xenos of the Orks. Beginning in 941M41, the Armageddon system was breached by a massive Ork hulk, it swept aside the defense systems of the system and made planet fall on Armageddon Prime. The Orks were led by the now infamous Ghazghkull Mag Uruk Thraka, who had united the five tribes of his work in a prophecy of unending war. The lord of Armageddon, the soon to be revealed incompetent and eventually traitorous, Hermon Von Strab refused to take the ork threat seriously and prohibited calls for assistance. It was only through the actions of the Imperial Guard Commissar Sebastian Yarrick that astropathic messages were sent out, an action that earned him the Lord's ire and saw him exiled to Hades hive.
Von Strab believed his PDF forces would be enough to see off the Ork threat and withdrew to Armageddon Secundus, believing the Orks could not cross the equatorial Jungle. He was proven wrong. Three ork tribes spilled out of the jungle, overrunning the stretched Imperial Lines. At this point Von Strab ordered the Titan Legions on Armageddon into battle to push back the green tide, despite the objections that they could not do this. The Iron Skulls marched into battle despite this and killed thousands of Orks before succumbing to the numerous Gargants the Orks brought with them, but not before the Princeps Prime Mannheim led his titan into the heart of the horde before his reactor detonated in cleansing nuclear fire.
With the titan legion gone, the Orks had little to oppose them and overran Hive Infernus. It was at hades Hive that the tide would turn. Under the command of Commissar Yarrick, he led the masterful defense, pulling more and more Orks away from the frontline into the siege of the Hive. Every attack was repelled and his presence boosted morale, holding the Imperial line. Eventually Gazghkull himself led attack after attack against the hive in an attempt to take it. Time and again he was thwarted by Yarrick until it was too late. Relief arrived in the form of three companies of Space Marines, most notably form the Blood Angels chapter led by Commander Dante, who took command of the war and place Strab under arrest, though he later escaped. The back of the greenskin assault was broken and Gazghkull driven back, but not before Hades Hive was overrun, the broken and barely alive body of Yarrick found among a pile of dead orks. Though it was thought that Gazghkull was killed, the rumors was false and he led counter attacks against Imperial forces until the Orks were able to make their escape upon their newly constructed starships. Though much fighting remained, the war for Armageddon was won.
This would prove to be only a temporary solace, as 57 years to the day, the Third war for Armageddon began in 998M41. During the 50 years between wars, the ork Warlord Thrakka had not been idle. He tested new Ork technologies and tactics throughout that time, constantly preparing for his next war. It began with raids and attacks in nearby systems in the sector, ever growing in frequency and violence, drawing more Imperial forces away from Armageddon. After months of attacks, the true invasion began. The largest ork fleet ever seen broke the warp in the Armageddon system, thousands of ships and hundreds of roks. The orks quickly swept aside the Imperial Navy and reduced the Imperial Naval facilities to damaged hulks, preventing their use by the Imperial Navy. As the fleet withdrew in an attempt to harry the orks and hold out till reinforcements arrived, the implacable ork advance broke through and made planet fall on Armageddon. In an act of vengeance, Hades Hive was obliterated from orbit by the decent of dozens of ork Roks, reducing the hive to a smoldering crater.
All was not lost, for Yarrick, the hero or Hades Hive had returned after 20 years of chasing Gazghkull to lead the defense. In the opening days of the war, millions of Orks made planet fall, overwhelming defenses and establishing their beachheads. The ingenious use of Roks, slowed down by modified tractor beams to establish bases and fortresses, with each equipped with ork tellyportas to bring forces to the surface. Rapidly, Hive Acheron, Volcanus, and Tempestora fell. The first fell to the treachery of the long thought dead Von Strab, who had returned with the greenskins with promise of returning to power.
Over the ensuing course of th war, the green skin advance was stymied byt not stopped. The war was looking to be lost despite the Steel Legion adn Commissar Yarrick's best efforts. Many ork Roks were destroyed and advances stopped, but the continued to come. It was the arrival of the Black templars and their fleet most importantly that stemmed the tide. Through multiple fleet actions, the Templars took command of Imperial Naval forces and claimed multiple victories over the orks, culminating in the destruction of the ork Space Hulk Malevolent Dread. Though bloodied, they succeded and were able to reduce the tide of greenskins making planet fall.
With combined actions of the Steel Legion and Space Marines, the ork advance was halted and Imperial control was maintained over much of the world. As the Stalemate began, the dread ork warboss left the Armageddon system in search of new conquests. The Black Templars and Commissar Yarrick pursued him, swearing to end the threat that plagued the Imperium. Though the orks have yet to be driven from Armageddon, the planet was in Imperial control and the hive factories churned ever more war material to face this threat. Orks continue to flock to the Armageddon system and the Imperium has yet to amass the forces needed to purge the Xenos threat once and for all, though it will come in due time.
It is Armageddon that stands, protecting the heart of the Imperium from one of the greatest threats it has ever faced. Should it fall, Segmentum Solar would be open to rampaging orks. Yet it stands as a bulwark against the tide, holding back the xenos that would destroy the Imperium. It is the Steel Legion and defenders of Armageddon that do this, dying so that the Imperium can continue, holding back the Xenos that would undo the Emperor's Great Work. It is to Armageddon and the Steel Legion should others look for the examples of sacrifice and courage necessary to hold the Imperium together in it's time of need.