Foreigners
The Hafn
The Hafn have surgeon-priests who are responsible for sewing together the citizens who are selected for service in logistical ships ca. Raven Stratagem. (courtesy of Eller)
The Hafn are fond of poetry.
The Lanterners
Before going to war with the heptarchate, the Lanterners were a client state that paid nominal homage to heptarchate calendrical norms and doctrine as well as actual tribute/taxes in exchange for a certain small degree of self-determination. This arrangement was originally negotiated, on the heptarchate's side, by some Andan who thought a diplomatic solution was best to protecting the heptarchate's sphere of influence in the region, and Lanterner leaders who were milking the situation for their own internal benefit.
The war happened because people on the Lanterner side came to power who wanted more autonomy than what the heptarchate was willing to give them. The Lanterners also spent some of this period of agitating building a coalition of like-minded neighboring polities (like the Gheffeu that get like a one-line mention in Ninefox).
The dominant Lanterner society has a class system that is largely based on birth, although it is not quite as extreme as a caste system (think British rather than India) and people can intermarry if they're willing to put up with the associated stigma. The military is one of the accepted means of social advancement, hence high-ranking officers being accorded a "courtesy" address of "kae" like aristocrats. Their primary language is distantly related to the high language, which perhaps helps explain some of the heptarchate's earlier leniency toward them.