Venerian Imperium

The Venerian Imperium is a human empire found beyond the borders of the Terran Commonwealth. Descendents of one of the lost human colony ships sent early in the Domus Diaspora, the ship found itself in slipspace and was sent back a hundred years into the past.

It is widely believed that they are sponsoring a number of influential insurrectionist leaders within its borders.

Domus Diaspora
The citizens of the Venerian Imperium can all trace their roots to the descendants of the lost colony ship UNSC Voyager that was declared 'missing with all hands' in 2304. Due to a miscalculation on the crew's part, the ship was caught by a temporal hole in slipspace, sending the ship back a hundred years into the past. Their ship crashed into the Veneri ocean, forcing its crew and any passengers on-board to leave the ship as the slipspace engine would explode violently once the water reached its core.

When the ship did explode, the survivors were lucky enough to have found land as the explosion had created a massive tidal wave that would've drowned anyone who was unfortunate enough to not be on land. After reminiscing on their loved ones, the survivors went to work on building a new society on Veneria.

Present
It is unknown when and how the Imperium reacquired its technology, but it became apparently very quickly to the Commonwealth that the Imperium had no intention of unifying with the Commonwealth. They greet the Commonwealth in open hostility. The Imperium's military is nothing short but astounding, but it falls behind in technology when compared with the Terran Commonwealth.

During the Insurrectionist Wars, ONI operatives were able to uncover a number of links between numerous insurrectionists groups and the Verenian Imperium. It is widely accepted by many in the government that the Verenian government is housing known insurrectionist groups within its territories.

Military
They are revered across human space for their intense relationship with the military. Children are recruited at an early age of 12 into the Astra Militarum as a way to ensure their absolute loyalty to the Deu'Rex and to the state. Their navy—the Astra Classum—is among the largest in the galaxy; but while they may possess a numerically-large armed force, their technology is relatively primitive when compared with the technology possessed by the UNSC.