In the year 3172, following a dozen-year-long secret expansion of their military, the fleets of Kanos rose to the skies in a massive offensive against the rest of the Core Cluster. Leaving their star, they quickly occupied and violently overthrew the existing government of Otionia, and began generating AI "warminds" using its Cradle. The plan was, with such brilliant digital strategists behind them, they could gain the power to overthrow the sector's remaining star systems despite their limited numbers.
For a time it worked, much to the Core Cluster's dread. The Kanos expanded next into the Pelasgon system, placing a deep-space strike station with which they started controlling traffic coming from sector-North - preventing Arm reinforcements from Shaina from flanking them. They knew that the biggest threat to their campaign was the Arm of Onditz, who at the time was tied up in territorial squabbles with Tournikiotis, and they thought if they could just claim Huertas - the Arm's main provider of starship fuel - they would have the last strategic advantage required to win. Sure enough, the Kanos navy entered the Madhavi system and began obliterating Huertas's mining stations with little resistance.
The Arm's Counteroffensive
What they did not anticipate was that, on hearing of the Kanos offensive, the Arm would immediately abandon any interests it had in Tournikiotis's own, less aggressive, expansion - and fly its entire fleet straight past the Madhavi and Kartik systems and directly into Pelasgon. Kanos warminds were prepared for such an event, but not when this was combined with a near-simultaneous arrival of Arm reinforcements from Shaina - drilling into system the exact same day as their main fleet.
To this day it is unknown how the Arm coordinated such a joint-operation so quickly from halfway across the sector, the Arm themselves simply confirming that it was "not a coincidence". But together, the Arm's combined forces obliterated Kanos's presence in Pelasgon, and then - ignoring the defence of Huertas - moved straight into Kartik, overwhelming the heart of Kanos's offensive through sheer force.
Once the Arm had occupied the homeworld, the Kanos surprised everyone by quickly admitting defeat and saluting the Arm of Onditz's victory against them. They offered to leave their occupied worlds and dismantle their navy to the limits that the Arm were previously enforcing, but the Arm wanted more - as far as they were concerned the Kanos could not be trusted to resist doing this again.
Aftermath
So over the next year the entirety of Kanos's naval fleet was taken apart, the warminds "decommissioned", their shipyards and capital city demilitarised and host to a constant watchful Arm presence, and any extraplanetary territories were forfeit and auctioned off - including their deep-strike space station in the Pelasgon system, which eventually became the entertainment complex known as Quiza Station.
The Arm themselves also paid for this war: apart from seriously crippling their Huertas operations for several years, the ground they lost to Tournikiotis corporate expansion has coloured the Core Cluster to this day - with several of the Tournik megacorporations being some of the only political entities to exert colonial influence across planets, despite the Arm's concerns that this could one day constitute its own kind of invasion.
In the end, the Kanos invasion claimed just over 130,000 lives - mostly military. The Kanos, despite being ruthless aggressors, seemed to have no particular desire to cause the deaths of those who lived in the territories they occupied. And whilst they did claim the resources of these places their primary goal by their own admission seemed to simply be to "test their strength" - a fact that many Kanos tout as evidence that the Arm's sanctions against them were, and continue to be, much too harsh.
