Chaos - Daemonic Incursions: In order for a daemon to break through into the mortal universe, there must be a breach of the barriers between Warpspace and the material realm -- a Warp rift. These are breaches in the fabric of reality that can vary in nature and size, such as the massive Eye of Terror or the Maelstrom.Sometimes these occur randomly; at other times, either mortals or the Chaos Gods themselves bring about their creation by some supernatural act. The size of the breach can vary tremendously, from a slight thinning of the dimensional walls to immense wounds in reality that allow the daemonic legions to invade en masse.At times when certain conditions like the appearance of a Warp Storm or a sorcerous ritual have weakened the barrier between the Warp and realspace, a daemon can possess a mortal and turn him or her into a living portal through which whole daemonic hosts can pass for a time into the material universe.These daemonic incursions can taint realspace severely, often twisting and reshaping whole planets until they are lost into the Warp, becoming a part of the Immaterium and thus transformed into Daemon Worlds. It is not surprising that the Inquisition's Daemonhunters, the Ordo Malleus, are granted unlimited resources and political power by the High Lords of Terra to deal with such terrible threats to the continued existence of Mankind.Often, it is the tumultuous movements of the Warp itself that create a break into the material realm, allowing daemons to spill through the resulting breach. This might happen by chance; events such as the onset of Warp Storms, Warp-Drive implosions or a rogue psyker's mind suddenly exploding with raw power can cause a rift to appear into the Immaterium.At other times, the deliberate rituals and blood sacrifices of Chaos-worshipping mortals can allow the teeming hordes of the Chaos Gods to smash through into the material realm. Sometimes, simple mortal suffering, death and misery on a massive enough scale can form a Warp rift that a daemonic legion might use as a portal.Some Warp rifts last mere solar hours, or even moments, for the nature of Chaos is ever impermanent. A daemonic army that has passed through such a rift can become trapped in realspace and will swiftly succumb to the constant leeching of the Chaos energy required to maintain its presence.Of these, the greatest and most dangerous Warp rift is the Eye of Terror, which has lasted for more than ten thousand standard years. The Eye can be seen as a purple-red bruise upon the firmament from fully half the worlds claimed by the Imperium.It was created by the birth of the Chaos God Slaanesh in the early 30th Millennium and is home to unnumbered Daemon Worlds fought over by daemons and mortals alike, the infamous Traitor Legions of the Chaos Space Marines amongst them.Another Warp rift of excessive magnitude is the Maelstrom, found near the galactic core and a haven for thousands of pirates and Renegade Space Marine Chapters.Other, less widely known Warp rifts exist, such as the Heart of Darkness near to the world of Atilla, the Storm of Judgement that engulfs almost all of the Caradryad Sector, Hell's Gullet, which threatens to swallow the Berillian System whole, and the infamous Screaming Vortex that marks the border between the Calixis Sector and the frontier of the Koronus Expanse in the Halo Stars.Random Warp rifts are often caused by Warp Storms -- roiling expanses of turbulence within the Realm of Chaos that are echosed in realspace, restricting Warp-dependent travel and communication. If they become focused or powerful enough, they can pull the fabric of reality taut or even tear it open. Completely unpredictable, Warp Storms can be isolated to single planets or expand to encompass whole sectors.One of the worst Warp Storms ever recorded in Human history cut Terra itself off from the rest of the galaxy for the entire 5,000-year-long epoch known as the Age of Strife. The unfortunate worlds in the vicinity of such a cataclysmic event can become the playgrounds of daemons until the storm finally expends itself.A few Warp Storms have endured for so long that they can be considered permanent, their self-sustaining energies trapping nearby planets and star systems in a quagmire of roiling Chaos.Without the Warp, there would be no psykers, no interstellar travel and no interplanetary communication. In fact, the Warp is essential to the survival of Humanity.Spacecraft travel through its shifting tides, capable of travelling thousands of light years in a fraction of the time a journey using conventional reaction drives at sub-light speeds would take. By such means, Humanity is bound in a single interstellar Imperium, led by the divine Emperor of Mankind.Through astrotelepathy and the guidance of the psychic mutants known as Navigators, the worlds of the Imperium are able to maintain their fragile bonds. The Emperor's will may be mighty, but His reach is long only because His fleets can travel through Warpspace, the fragile bubbles of reality that protect each warship held up by complex Geller Fields and raw faith.While Mankind would have a fraction of its current numbers and strength without the Warp, Chaos in its turn would be much diminished without the presence of Humanity in the galaxy. The Chaos Gods drink emotions and thoughts, growing bloated with psychic power in the process. Over the millennia, each has fed on an aspect of Human nature: rage, desire, corruption and inconstancy.Strengthened and moulded by the collective thoughts and emotions of the inhabitants of reality, the Dark Gods nurture in Mankind those same passions that sustain their very existence. As Humanity has spread across the stars, its numbers have grown immeasurably, fuelling the Chaos Gods. So the circle is established, with mortal follies and weaknesses feeding the Dark Gods and those same gods then encouraging Mankind in turn to further follies and weakness.Humanity has long been able to use the power of the Warp -- magicians, seers, witches, mediums, shamans and exorcists have all trapped into its power across the breadth of Human history, albeit often unwittingly. Psykers such as these manifest their powers by drawing upon the Warp, siphoning its unnatural energy to hurl blasts of energy, teleport objects, send their thoughts across space and time and perform countless other "miracles."Once, the gift of true psychic power was confined to only a few helpless individuals who usually fell victim to superstitious prejudice in Mankind's distant past. However, the number of psykers is rising in the galactic population of Humanity with every passing century.This constitutes a profound evolutionary change for Mankind. Every time a psyker draws upon the Warp, he disturbs its natural flow, creating an eddy that may simply die away or be fed by other movements until it becomes a raging tempest that feeds a Chaos God. Each psyker causes a pinprick of disturbance within the Warp; each can be the seed of a Warp Storm; each can rouse a Chaos Power to unthinkable conquest.The invasion of a daemonic army is analogous to hell being unleashed upon reality. Free from the physical limitations of a mortal force, a daemonic legion can appear and disappear at will. On occasion, it will mass for a great attack; at other times, individual packs of daemons will hunt across the affected globe, terrorising the populace, randomly enslaving and killing.Those mortals with even the least psychic potential suffer first as the influx of Warp energy releases the latent power of their mind, immolating them with magical fire, turning them into rocky statues, or causing their brains to simply explode. Poltergeist activity and random bursts of pyrokinesis can ruin buildings in an instant. People hear deranged screams and lurid whispering whilst unnatural stenches taint the air.A daemonic invasion is all but impossible to stop by conventional means, for the very act of warring against daemons feeds the psychic power keeping them in realspace with fear and hatred. Only the closing of the Warp rift can deprive the daemons of their power.Often, there is nothing that can be done but battle against the incursion until the Warp rift runs its course. Battles fought against a daemonic incursion are utterly different than those against mortal foes, for defensive structures and garrisons have little to no effect. To wage war against invading daemonic hosts, an army must be ready to respond to the most sudden appearances of its adversaries.To compound matters, the motivations behind daemonic incursions are unfathomable. Even the Tyranids, who are so alien as to be beyond the ken of man, war for sustenance and survival. Instead of these base drives, the objectives of a daemon commander will often be completely obscure -- they might be to slay a million mortals, to retrieve a single artefact, or to kill the grandchildren of those that once banished them back to the Warp.Other times, the daemons have no goal or plan at all, and the gibbering creatures of the Immaterium make decisions according to opportunity and their intrinsic nature.