Xenos - Major Xenos Races: Though there have been hundreds of sentient species in the galaxy's long history, only a handful have ever managed to build vast interstellar empires beyond their respective homeworlds. Even fewer have ever been powerful enough to rule the galaxy for any length of time.While Humanity is the current dominant species of the Milky Way Galaxy, it was not the first, and it is constantly challenged from without by rival species who envy its position of power.What distinguishes these races from the myriad of lesser intelligent species is the fact they are all currently too powerful for the Imperium of Man to exterminate like so many others:Asuryani - The Asuryani, also called Eldar or Craftworld Aeldari by some, are an ancient, but dying humanoid race whose technology remains far more advanced than that of the Imperium. The Aeldari once possessed a galaxy-spanning empire that exceeded even the Imperium of Man in size and strength. After the Fall of the Aeldari shattered their civilisation, the Aeldari were reduced to a refugee population as the majority of the race now exists in worldships known as craftworlds drifting across the galaxy. These Aeldari refer to themselves as Asuryani, "the children of Asuryan." The Asuryani hold Humanity, or the "Mon-keigh" as they refer to Humans, in disdain as it was the death of their empire that allowed Mankind to rise during the Great Crusade, yet they also assist the Imperium against common foes like Chaos and the Tyranids whenever it suits their own purposes.Drukhari - An off-shoot of the Aeldari race with its origins before the Fall sometimes inaccurately called the "Dark Eldar," the Drukhari differ radically in culture if not biology from their Asuryani cousins. Centred around the Dark City of Commorragh which is located within the ancient Labyrinthine Dimension of the Webway, the Drukhari are a depraved society characterised by sadistic violence and hedonistic excess who continue to indulge in the same vices that caused the Aeldari Empire's Fall. They are sustained by absorbing the psychic suffering of their victims and slaves, who they acquire from all the other intelligent species of the galaxy during raids from the Webway into realspace. Humanity often fails to make a distinction between the Asuryani of the Craftworlds and the Drukhari as the two can appear anatomically and technologically identical, though the cultural distance between them is actually vast.Necrons - The Necrons are a race so old that even the Aeldari would consider them ancient, possessed of technologies so advanced they defy the comprehension of the Imperium's best savants. The Necrons have lain dormant deep beneath their Tomb Worlds for millions of Terran years. They have only begun to reawaken in the last few centuries of the 41st Millennium. Robotic and virtually indestructible, Necrons have been emerging from their ancient Tomb Worlds across the galaxy to slaughter and kill the unsuspecting denizens of the galaxy, determined to reestablish their ancient galactic empire and eliminate all of the lesser races that have taken their rightful place.Orks - The Orks are a hyper-violent species of hulking green-skinned humanoids who have existed as long as the Aeldari, yet continue to be a powerful force in the galaxy due to the durability of their own biology, if not their civilisations. Universally perceived as a crude and savage species by all of the other intelligent races of the galaxy, this is for the most part an accurate assessment. Often fighting for the sheer sake of the joy they find in violence, the Orks are in a constant state of war with the other races of the galaxy and themselves. Due to the peculiar adaptability and efficiency of their reproductive spores, Orks may be the only species in the galaxy truly immune to extinction, and are more akin to an infestation than a species.T'au - The T'au are a young race of alien humanoids from the Eastern Fringe of the galaxy who have created a rapidly expanding interstellar empire with highly advanced technology in only a few Terran centuries. Led by the mysterious Ethereal Caste, the T'au are compelled by their pseudo-religious philosophy known as the Greater Good to expand their borders until they have assimilated and imposed their collectivist ideology upon the entire galaxy. Unique amongst the other major intelligent races of the Milky Way, the T'au Empire effectively employs a combination of diplomacy and measured military force to acquire other intelligent species as allies to their cause. Though barely a blip on the galactic map when compared to the vast interstellar territories that encompass the Imperium, the T'au Empire poses a realistic threat to seize the frontier of space away from Mankind if something is not done to counter their continued expansion. Even many Human worlds of the Imperium have found the Greater Good an attractive enough philosophy to turn their back upon the dictates of the God-Emperor.Tyranids - The Tyranid species -- actually a collection of different bioforms all genetically engineered to serve specific functions by a psychically gestalt Hive Mind -- currently presents the greatest threat to the Imperium and every other intelligent race of the galaxy. The Tyranid menace comes from the great void beyond the boundaries of galactic space to strip all the life-sustaining planets of the Milky Way Galaxy of their precious bio-mass in a quest to constantly improve and evolve their species towards new heights. Ever evolving and learning to adapt to the tactics of each new foe, no less than nine Tyranid Hive Fleets have been identified by the Imperium of Man entering the galaxy. Several of these Hive Fleets have yet to be destroyed or contained, while others have been shattered through immense expenditure of lives and resources, only to see new Hive Fleets emerge from the splintered remains of the old. Despite the tremendous military investment already put forward against them, it is feared that all Tyranid incursions thus far have merely been the vanguard to the truly massive swarm that is even now approaching the galaxy. If all projections prove accurate, then the coming threat may prove to be the deathblow to the already crumbling and over-taxed Imperium and may represent a threat to all other lifeforms in the galaxy.