Cleansing of Laeran
The Cleansing of Laeran is the name given to one of the most notable military campaigns of the Great Crusade.
Scouts from the Emperor's Children Adeptus Astartes encountered a hitherto-unknown xenos race, the Laer. Analysis of captured scouts and envoys showed the Laer to be concentrated in a single star system, dubbed Laeran. Like the Emperor's Children themselves, the Laer prized perfection in all aspects of civilisation; by the use of chemical and genetic manipulation from birth, individual Laer were adapted to their roles, whether they be workers, soldiers, even artists. Observers from the Adeptus Administratum wondered if perhaps the Laer might be made a protectorate of the Imperium as conquering such an efficient race could prove to be a long and costly endeavour.
Fulgrim refused any notion of co-operation. Only Humanity could be perfect, he insisted. For xenos to be comparable was basely offensive, and the Laer deserved nothing less than annihilation. He ordered his Lord Commanders to attack immediately, beginning a war that the Administratum predicted would last decades. Fulgrim heard this prediction, and shook his head. In one month`s time, he said, the Eagle would rule Laeran.
In every theatre of war the battle was joined. The Emperor's Children attacked the Laer amongst the stars, in their cities, beneath their oceans and over the hulls of their orbital platforms. Everywhere they faced enemies adapted to their conditions - warships connected bio-electronically to their crews minds, liquid-breathing sea warriors, scouts capable of moving as fast as a Land Speeder, gunners whose eyesight allowed them to target individual Space Marines in squads miles distant. The casualties on both sides were horrendous - it is estimated that, if not for the excellence of the Legion's Apothecaries, more than half of its warriors would have died from their wounds.
The Laer never surrendered - their last warriors died fighting in the ruins of their capital city. One month after he had begun the attack, Fulgrim planted a standard displaying the Imperial Eagle over their corpses, leaving it the only thing standing on the worlds of the Laeran system. Over 700 of his men were dead, 6 times that number injured, but Fulgrim believed he had proven himself correct. Against some of the most finely-honed alien warriors ever encountered, humanity had proven itself more powerful.