The Pegasus Gulf is a backwater frontier sector on the Eastern Fringe just between Ultramar and the Tau Empire. Consisting mostly of low-population colony worlds on still-wild planets, the Gulf is not heavily tithed. It’s crown jewel, the shrine world Ulyssia, was attacked by a wayward splinter fleet decades ago and the planet was declared Exterminatus by Battlefleet Pegasus. Since then, the only two truly notable colonies in the Gulf are the fortress world Heavensreach at the heart of the Gulf, and Persephone, the largest agri-world in the sector and the breadbasket of the colonies.
Now, it is the year 005.M42. The Cadian Gate has been breached by Abaddon’s 13th Black Crusade. The worlds encircling the Eye of Terror have been razed to the ground, and his fleet race towards Terra like hounds on the hunt. Hive Fleet Leviathan rises like a sea beast from below the galaxy, devouring sector after sector as it wriggles towards the shining light of the Astronomican. No one is coming to save the Pegasus Gulf. Despite what its billions of inhabitants want to think, it is an inconsequential region of space.
Persephone has fallen. The north-western expanse of the Gulf has been conquered by the savage greenskins. Mankind has fled to the coremost worlds. The Hades Gate grows more unstable with each passing day. Long-dead Tyranids are supposedly rising from the dead, and a dynasty of Necrons crawl from their shallow graves. Scheming Eldar and expansionist Tau fleets bear down on unprotected worlds, planting their banners of victory on blood stained soil. All the while, xenos pirates and raiders leave the shadows they were forced into, and heresy begins to spread amongst the terrified populace of the Gulf. Civil war has consumed Tempest, and declarations of colonial sovereignty have spread across the Homestead Marches and Iron Cluster like wildfire.
To the south, Sprawl has declared autonomous rule, and there are whispers that the heretical non-Imperial humans that have inhabited the Harvest Federation since before the Great Crusade are openly consorting with orks. The neighbouring Vandal Reach seeks to expand its borders as overpopulation runs rampant in their core worlds. Ultramar seeks to add another protectorate sector to its holdings, should the Imperium fall. The bureaucrats and nobles on Heavensreach are clinging onto their colonies with desperate fingers. All the while, the Imperium at large ignores the backwater plights of the frontier, and no news has been heard of Abaddon’s advances or the state of the core Imperium for nearly six years.
This is Warhammer 41k, and there is only war.