The Zadoc subsector in 008M42 was the key link in the entire sector to the rest of the Imperium. Since the loss of the Aleph subsector to the rebel UFP, the Zadoc subsector now became the very border between the Empire of Mankind and the ever growing Tau Empire.The subsector itself consisted of six major planetary systems ruled nominally from the capital Zadoc. Libria, the most populous system was recovering from a tyranid invasion,and Tyranteous and the Sisters (Alphe and Betor) were sparsely populated Agri-Worlds. Zadoc and Tarsis Major were the two most important worlds, heavily defended and protected by the substantial Zadoc subsector fleet.
These were not the only worlds, just the most important. Off the major space lanes lay many more worlds, some Imperial, some neutral and others alien or unexplored. The centre of the subsector harboured the large expanse of space covered by the Mabb Nebula, where Forts Aerin and Sparcos stood guard against Ork forrays from Kallack. Deeper into the nebula Imperial agents knew lay other more hazardous threats, including the Eldar and Necrons.
Hubward of the subsector lay the Perseus Deeps, a lawless area of space. Grimlock, on the edge of this wilderness, had long since fallen from the Emperor's light, and Chaos raids were common. The key link in the chain of defences was Caitlen station, a vast and heavily defended system of space stations and shipyards. It was here that the subsector fleet spent much of its time.
Two areas of smaller planets held the key to the subsector. Towards the galactic core the Rim world, on the edge of the Perseus Deeps, mainly neutral worlds or small outposts, provided an ideal base to launch a crusade either into the Deeps or the other way, into the core of Imperial territory. The Shadow worlds, a similar set of small outposts and mining ventures, lay on the edges of the Mabb nebula, and would always be on the front line of any escalation of hostilities.
In mid-008M42 the various factions in the Aleph sector were not strong enough to launch any campaign against each sides' main worlds. Melberg had drained the Imperium and the Tau, while the very lack of Eldar numbers meant conquest of an Imperial world was simply out of the question. Instead each side sought to gain influence, through diplomacy or terror, over the Rim and Shadow worlds, to build up their forces for the next phase of operations.
The Tau favoured separate approaches, led by the water caste, but backed up by the might of the fire caste. Elan Ro was sent into the Mabb nebula, while Shadowstrike headed for the Rim worlds. The Tau hoped to win over the worlds in the Zadoc subsector in order to isolate, and then acquire the major worlds. However, they were under no illusion that this would be easy, but after Melberg an all out shooting war with the Imperium was unthinkable.
The Dark Angels also headed into the Shadow worlds, investigating reports of Necron and alien activity, as well as following their own mysterious agenda. The Imperium as a whole mainly acted through the Inquisition, who were determined to put a stop to the Tau encroachment on Imperial territory, as well as rooting out backsliding and laxity on the part of the Imperium's forces.
The mad Chaos Admiral Thok also intended to make his mark, and his ambitions turned to the Rim Worlds, with the final intention of taking Caitlen station and the valuable shipyards. From there he could gather enough support to launch an attack on his old enemies... Whoever they were.
The Eldar meanwhile were disturbed by the idea that the myriad aliens of the sector should be encroaching on their realm. The Mabb Nebula shielded a number of exodite worlds which they did not want discovered. In addition the nebula contained several Necron Tomb worlds, and the Eldar were convinced that the stupid blundering races infesting the area would no doubt wake them up. In the Perseus Deeps the Eldar were also concerned with the actions of Grand Admiral Thok, someone they would even ally themselves to the Imperium if that meant stopping his insane antics.
And then there were the Orks. For to long the Vork Ork Empire had been left in relative peace. Now like a plague or infection the Orks had multiplied so that their Warlords now had to look outside their borders for new conquest. Ork raids increased and it was only a matter of time before events escalated into a full blown Waagh! The Ork Warlord Nutbasher began his crusade on the very fringes of the Mabb nebula, clearly intending to break the stranglehold on the Ork world of Kellack.
Finally, though beaten and fragmented, the Tyranid Hive fleets moved steadily north east, and from their attack on Libria the Imperium reasoned that they would next fall upon the Rim Worlds. New Sparta and Rhesius would feel their presence first, and to protect them the Imperium sent out patrols, but could not locate the Hive fleets in deep space, much to the frustration of Admiral Jellicoe.