The Carolignia Kingdom started before the Days of Fire and Fog as a social club dedicated to medieval re-enactment. After civilization ended, that gave the original leadership a core of people who could survive using low-tech methods and a small group of people who had at least some familiarity with wearing heavy armor and fighting. The early leadership leveraged those advantages to help survive during the worst days of riot and famine.
Over the years, the leadership of the Kingdom became increasingly technophobic and aggressive. The second King took the view that advanced technology, and especially electronics, was the cause of the Fall, and forbade their use. His various successors have kept that view, at least officially.
The Kingdom has the largest population of any polity in the Commonwealth, and is often a menace to their neighbors. They have conquered several members of the Pilgrim's MMA, most notably Patriot City, and enslaved the former villages as serfs on the farms. They would be more of a threat if not for paranoia and instability at the top: while there have only been two successful coups in 70 years, the threat of coups keeps the Kingdom military constantly in a state of confusion and suspicion. Much of the army is also used to maintain order on the peasant farms.
The Kingdom does not forbid trade, but does require that all trade been funneled through the Royal Assessor in Patriot City, who takes a 20% cut of goods sold by outsiders. Foreigners can enter the Kingdom anywhere as long as they head straight to Patriot City, and may leave from Patriot City in any direction, but any strangers found in other parts of the Kingdom are subject to arrest and enslavement.
The Kingdom also aggressively patrols the area around Uxbridge Farms, in an attempt to starve the robots there of supplies. The Kingdom doesn't dare attack as long as the Defense Bots are active, and hopes to wait until they collapse from lack of spare parts before moving into take the best farmland in the Commonwealth.