Cancridrean Periphery

"The tide still laps against the shore, questing for faults, degrading all it touches. Listen close and you can almost hear its laughter..."

- From the banned historical treatise: The Forbidden Frontier, Author Unknown

Trapped between the very border of Imperial-held space and the disputed territories of the hostile Amphra xeno-species lies the Cancridrean Periphery, a fractious demi-sector forged in the sputtering fires of a failed Crusade. Here mankind's dominion is tenuous at best, the Astronomican's light dim and feeble, all manner of undesirables congregating within its fetid underbelly even as things eons older than humanity prowl the darkness in-between stars...

Origins
Mechanicus astrophysicists have frequently theorized that the primordial expanse now known as the Cancridrean Periphery did not form naturally, but rather was created eons ago, when a dwarf galaxy collided with the Milky Way. This cataclysmic event would certainly explain the sheer abundance of stellar anomalies present within the Periphery, from unstable star-nurseries to hyperdense nebulas and fluctuating globular clusters. With these astral formations making space travel through this area all the more hazardous, the Periphery remained relatively divorced from the civilized galaxy for untold millennia. Reportedly, a colonization effort was attempted by the 228th Exploratory Fleet during the early years of the Great Crusade, but the the expedition was ultimately cut short after a failed attempt to populate the far-flung planet Amphr, homeworld of the warlike Amphra.

Eventually said area was classified by the Imperium as the Cancridrae Sub-Sector, a sparsely-populated fringe bordering the more populous Mazul Star System. Said Sub-Sector was paid little mind until M.39, when the Amphra Matriarchy, having finally crossed the threshold into Imperial space, began raiding and pillaging outlying settlements. This led to a subsequent retaliation by the Imperium of Man, culminating in the disastrous Siege of Korinthos, in which the Amphra utilized Exterminatus-grade orbital munitions to ionize the Agri-World's atmosphere, scouring the planet's surface in a thermal hellstorm.

Cancridrae Xenocide
In retaliation for Korinthos, the High Lords of Terra themselves ordered a massive Crusade to be undertaken. A massive force, consisting of no less than twenty different Imperial Guard outfits, three Adeptus Astartes strike forces, and an entire Battlefleet, were mustered to persecute a singular cause; the eradication of the Amphra. This campaign, officially labeled the Cancridrae Reclamation Crusade but more infamously known as the Cancridrae Xenocide, lasted little more than four years. A combination of internal strife, materiel shortages, sheer distance from the Imperial commonwealth eventually cause the entire endeavor to come to a bloody, screeching halt by 006.M40.

Granted, the Xenocide was not an abject failure, as the Amphra were driven back and many planets were either recaptured from the Amphra Matriarchy or brought into the fold. In 124.006.M40, a massive reconstruction known as the Revanchist Initiative was undertaken under the aegis of one Magos Titus Antiochus Rho-16. Backed by the Adeptus Mechanicus and overseen by the Adeptus Administratum, the Initiative succeeded in its goal of fortifying the Sub-Sector's infrastructure and soon after was declared a full Sector in its own right, absorbing part of the Mazul-Cancridrae Border into its own territory, with the revitalized world of New Korinthos as its Sector Capital.

Present Day
The Periphery's relative isolation has spared it from much of the turmoil that has wracked the galaxy over the millennia, but said isolation has in turn fostered new a whole slew of problems. Dissident, independent factions, such as the criminal Caebolg Syndicate and the heretek Phantasmagorians erode the sector from within. The Necrons of the Indrahkt Dynasty, aboard their void-borne superfortress Brahmastra, continue to devastate Imperial settlements and then vanish without a trace, and with each passing year the Amphra grow bolder in their raids and skirmishes.

Only time will tell if the Cancridrean Periphery will continue to persist against the encroaching darkness, as it has for a millennium, or be consumed by it...