Power in Rasenna is shared between two institutions: the princes who govern the principalities, and the Great Houses who run much of the business and drive most of the laws. Technically, Rasenna is a republic, and when a prince comes to power by means other than open warfare, it’s through election. The wealthiest voters, and those who have the most influence, are the Great Houses.
The Great Houses are the aristocracy of Rasenna: not quite nobility, but the foremost citizens of the nation. Most are merchant houses, having established their power via the amassing of wealth during some portion of Rasenna’s history. The majority are also familial in aspect, passing House status onto their offspring and expanding their influence through marriage. Most Houses may also adopt exceptional people into their ranks by means other than marriage; such members are often distinguished as “cadet members.” The exceptions are a few Houses that have an almost meritocratic approach to membership (in particular, the Sorcerous Houses) and those that were established to promote the welfare of immigrants or racial cultures within the nation (such as the dwarven House Graelskeld).
Each Great House has a House Grandfather or Grandmother, the chosen representative and head of household. This figure may not in fact be in tacit control of the entire House, but is considered its head for all purposes dealing with those outside the organization.
Possessing the lion’s share of wealth and power within Rasenna, the Great Houses would almost rule the country with an iron fist. However, a few things keep them from exercising complete control. For one, they’re often lacking in the love and esteem of the common man, and a Prince with a history as a war hero or a benevolent and generous ruler is very difficult for a Great House to oppose. For another, many of the true powers in the realm are hard to buy: although the Sorcerous Houses are able to keep a close rein on most of the arcanists in Rasenna, individual magi can still rise to surprising levels of power — to say nothing of empowered priests or talented mercenaries.
And most importantly, the Great Houses are far from a united front. They constantly quibble, plot, duel, declare vendetta, scheme and even go to open war amongst themselves. Only two things ever seem to unite the Great Houses: clear and undeniable threats from without the nation, and one of their own rising to particular prominence. In the former case, they will set aside minor differences temporarily to make certain that the nation isn’t overrun or choked off from its vital trade. In the latter, the Great House that steps too far out in front of its fellows is exposing its back to countless jealous knives.