The Coalition force colonized a world long before the Fleet found New Canaan. They call it Home. This world is rimward from New Canaan, this is the reason for the name Outsiders. When explorers discovered their presence a few centuries later they coined the term for this the only human society outside NC.
Home happened to be located in an a region full of conflict. The Polder saw this region as their own and were fighting a long and losing war against multiple encroachers. They responded to this new appearance of an alien presence with force. The Polder stayed hidden from the Outsiders until their military was ready. They attacked in force and in a great battle defeated the Outsider fleet which had carried them from Sol to Home. Home was occupied by the Polder. Their occupation was not cruel, it was indifferent, but it scarred the Outsider psyche. Revolt simmered and the Polder weakened, their resolve crumbled as they gave ground to the encroachers in other systems. When the garrison was sufficiently weakened the people, most of whom were marines and navy personnel from Sol, slaughtered those remaining. The Polder fleet withdrew.
This occupation, combined with the destruction of civilization at Sol, has turned the Outsiders into xenophobes. They rebuilt their military. In the interest of effectiveness they rediscovered the AI, and incorporated them into their navy.
The Polder tried to send warning, but the Outsiders would not listen, wary of Polder trickery. A powerful AI "race" exterminated life on planet after planet in the region. When they faced the AI operated ships of the outsiders, the Outsiders found their defenses would not defend them. They attacked Home quickly, bombarding them from orbit, and nearly wiped out the entire population.
The current population of Home grew up in the wreckage, and have vowed never to be too weak to defend themselves again. They are suspicious of AI, and use only limited forms themselves now. They are a militaristic society, advocating the virtues of discipline, strength and victory through combat.