In 999.M41, war came without warning to the Agripinaa Sector, and the opening moves by the Forces of Chaos saw large numbers of plague-ridden Space Hulks entering Imperial space. Though many were intercepted by the Space Marines and destroyed, some managed to escape the Astartes' attention. Some of these foul vessels of contagion found their way into the Agripinaa Sector, spreading their disease and pestilence amongst the masses throughout the sector. Along with the adjacent Belis Corona Sector, they were some of the first to bear witness to the rise of hordes of infectious, undead zombies that threatened billions of people on many of the Imperial worlds within the sector. This plague was later named the Plague of Unbelief.