The invasion began 250 standard years after the First Tyrannic War and the destruction of Hive Fleet Behemoth by the Ultramarines on their homeworld of Macragge. An armed presence had been maintained in the galactic southeast, which members of the Imperium's Adeptus Administratum began to question the need for, arguing that Behemoth had been the sum total of the Tyranid race's expansion into the Milky Way Galaxy. When worlds along the Eastern Fringe of the galaxy began to erupt in rebellion, terrorism, riots and sabotage, the same Adepts claimed the people were dissatisfied with living amid an armed camp.