A human colony, originally an independent world in the Near Terminus called Patthu. An agricultural world, it had perfect garden conditions, was resource rich, and by the 2160s supported a population of some millions, mostly batarian. The planet was considered out of the way enough to avoid big players menacing it, and close enough to Hegemony space to enjoy the amenities of life (like a functioning comm buoy system).
This idyllic existence ended when a human government moved in. A couple of thousand humans established their rule over the colony. These were mostly Systems Alliance deserters, human supremacist types unhappy with humanity’s new relationship with the Citadel, and social dissidents who saw the success of the nearby Sultanate and thought that they too could establish a functioning colony. They started building factories, pressed the locals into service, and renamed the colony New Carthage.
Outside their own star system, people were unaware of the takeover. As far as the rest of the galaxy was concerned, Patthu was marginally more quiet than normal and yet another group of upstart humans had moved through the Terminus for reasons unknown.
By 2175, New Carthage was a proper colony. They poached some talent, freed or stole slaves to supplement their population, and had begun heading up development projects of their own. They come out with unique ship designs using bizarre parts only manufactured at their factories on New Carthage, so as to slow down attempts to reverse engineer and mimic the designs by third parties. While nominally a neat idea to keep their edge for as long as possible, it meant that their commerce raiders went from being background noise in the piracy statistics of dangerous areas to a readily identified, specific threat.
While the mysterious, decidedly human force attacking everyone’s shipping with never-before-seen strike craft wasn’t particularly dangerous to any polity, they were an annoyance and, more importantly, the technology implied that there was a single backer with an agenda that involved attacking everyone else. Custom fighter designs and the like aren’t an option for an average raider group, nevermind the bizarre manufacturing requirements of New Carthage’s interceptor and bomber designs. All that was known was that the culprits were humans and captured flight computers indicated that they were based out of an outpost called ‘New Carthage’. Common wisdom was that they were Alliance - Corsairs or sponsored raiders, striking in revenge for piracy attacks in the Traverse by hitting entirely uninvolved people throughout the Near Terminus. The Terminus Systems are never very happy about Citadel nations meddling, especially a jumpy upstart that doesn’t know better, so all involved were pretty keen on wrecking whoever was responsible despite the raids being, overall, pretty minor.
In 2178 this resulted in a multinational team being assembled to figure out what was actually going on and retaliate. This alliance included Lessan Vadarat, a frigate flotilla from the Sultanate and forces from Grainar, a minor Traverse power, which also hired on some human Privateers to assist. It would later be revealed that the Privateers were, in fact, Alliance Corsairs and that New Carthage had been raiding the Alliance as heavily as they’d been raiding everyone else.