Humanity alone, the Imperial Creed teaches, is the sacred form of intelligent life chosen by the God-Emperor to spread out amongst the stars.

These sentiments of xenophobia have been reinforced by the Imperial Creed, which preaches that Mankind has a divinely-inspired manifest destiny to be the sole ruler and inhabitant of the galaxy. In that time, many more alien civilisations have been discovered and destroyed regardless of threat level, culture, disposition, or technology. This policy of unconditional hatred persists into the modern Imperium more than 10,000 standard years after the Great Crusade ended in the blood and fire of the Horus Heresy. Other instances, such as during the Imperium's first encounter with the Human-alien alliance known as the Diasporex, would end in violence because of the inherent distrust the Imperium had for all alien civilisations even if there was common ground that could be found. The Imperium of Man's extreme xenophobia and outright call for genocide against all other intelligent species in the galaxy is in some ways justified by the sheer hopeless belligerence of most xenos races encountered since the Great Crusade.ДЄlmost all alien species encountered by Mankind since the Emperor first began to push His forces out amongst the stars have been so malevolent or aggressive toward Humanity that any form of negotiation or parley often proved impossible. Certain aliens, such as the Aeldari, who were more technologically advanced than the Imperium were often simply left alone so long as they did not threaten Human interests. This would also apply to the majority of Human civilisations encountered during the course of the Great Crusade like the Interex and Diasporex, which had founded cultures where alien and Human populations had successfully integrated into a single whole.Дiplomacy was rarely tried, and was more often offered only to other Human civilisations encountered in the course of the Great Crusade. Thus many species suffered extinction at the hands of the newborn Imperium which perpetrated one act of genocide after another. The Emperor believed that only in unity - unity bought at nearly any price - could Mankind survive a galaxy that was far more dangerous than any Human scholars of an earlier age would have believed.ДЄt its inception, the Imperium of Man made one of its core objectives the extermination of all alien life forms that posed any threat to Humanity. The scattered outposts of Mankind would be preyed upon for millennia by various xenos species, pushing the Human race towards eventual extinction until the Emperor of Mankind revealed his existence and began his galaxy-spanning Great Crusade to reunite Humanity under a single interstellar government. When the Age of Strife began with the collapse of the first Human interstellar civilisation, many suddenly isolated Human colonies were set upon by all manner of hostile aliens, though a few notable exceptions of peaceful coexistence occurred as well. The first Human interstellar civilisation which existed at that time made contact with many alien races, possibly including the Aeldari and the Orks, but the majority must have been hostile or incapable of co-habitating with Humans as no aliens are known to have ever willingly integrated into the broader interstellar Human civilisation of this time. It is not recorded exactly when the Human race learned that it was not alone in the galaxy, or which intelligent alien species it first made contact with, but what is known in early Imperial records is that Humanity has been competing with xenos since the Age of Technology. Lord Militant Tarkus Hol in his memoirs, Observations on the Inevitability of War Only the dead have trusted the alien, although the last may be deluded into claiming that they yet live.'

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