I shall rundown the history of the warp, here is some basic information of the warp from the wiki:
The Immaterium (also referred to as the Empyrean, the Aether, the Sea of Souls, the Realm of Chaos, Warpspace or most commonly, the Warp) is an alternate dimension of purely psychic energy that echoes and underlies the familiar four dimensions of the material universe. It is the source of all psychic powers and known instances of so-called "sorcery" or "magic" as well as the home dimension of the Chaos Gods and their myriad daemonic servants. In fact, the terms "Chaos" and "the Warp" are often used interchangeably by those aware of their existence within the Imperium of Man. Superficially, the Immaterium is Mankind's solution to the problem of faster-than-light travel, an equivalent to the Star Wars universe's dimension of hyperspace. This function as a faster-than-light medium for space travel is achieved because the Immaterium is a domain of pure psychic energy, with spacecraft navigating between its currents, as in an ocean. The psychic energy that makes up the Immaterium is believed to be the direct result of the existence of sentience in the universe, in particular the intelligent species of the Milky Way Galaxy. Considered to be a dark reflection of the material universe, the Warp is an ocean of chaotic psychic energy, raw emotion given physical form. Stirred by emotion and action, the Immaterium is the true Realm of Chaos, home to the Dark Gods who comprise the Ruinous Powers and their legions of daemonic followers. The Immaterium is also rumoured by many cultures, human and xenos alike, to be the final resting place of the spirits of the dead, and therefore can be considered the "Underworld" of the Warhammer 40,000 universe.
Here is some basic info on the wars of Armageddon
The Second War for Armageddon is the second of three massive conflicts between the Imperium of Man and the Ork Warboss Ghazghkull Mag Uruk Thraka that took place between 941.M41 through 943.M41. The war was fought on the Hive World of Armageddon in the Segmentum Solar, where Ghazghkull Thraka launched an Ork WAAAGH! consisting of five separate Ork tribes in an attempt to seize the planet for themselves. Three Space Marine Chapters were involved, including: the Blood Angels, Salamanders and the Ultramarines, along with dozens of regiments of the Imperial Guard as well as a large contingent of Inquisition forces from the Ordo Xenos composed of Squats. A notable effect of this invasion resulted in Ghazghkull earning the wrath of Commissar Yarrick, who dedicated his efforts after the Second War to hunting down Ghazghkull, with little success. The main war lasted for only two standard years, but continuous combat took place between the various forces for another next twenty years until 961.M41, a colossal effort between both factions for the control of a single, highly strategic planet.
The Third War for Armageddon that began in 998.M41 was a massive conflict between the Imperium of Man and the largest Ork WAAAGH! ever raised, led by the Greenskin Warlord Ghazghkull Mag Uruk Thraka. The war was fought on the Hive World of Armageddon where Ghazghkull Thraka had launched his first attempt to seize the planet exactly 57 standard years before. The conflict eventually drew in portions of over 25 Space Marine Chapters, dozens of Imperial Guard Regiments, several Titan Legions and caused immense destruction to Armageddon before essentially ending in an extremely narrow Imperial victory, though neither the Imperial nor Ork forces were able to secure complete control over the contested world and fighting is still ongoing in many regions.
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