There are 76 families of varying degrees of power, size and influence; most of whom can trace their lines back to the founding of Waterdeep itself. The power base in the North lies in the control of the flow of trade in and through Waterdeep. Waterdeep is the portal through which the riches of the north can be reached. Once trade from the south reaches Waterdeep it is routed to nearly anyplace in the north by mandate of the Lords of Waterdeep and by extension, the noble houses.
As with most large cities; information is also a currency that has its own exchange rate and houses that broker information or the art of misinformation are top tier families. Mercenary companies are common place and function as private armies and personal garrisons for a variety of different causes and organizations. Houses with mercenary services or training are second tier in the Waterhavian aristocracy. Caravan mastering and ranching comes in as the next tier; the north is rife with creatures domesticated and wild; docile and hostile.
From the lone hedge-wizard who hires a couple of mercenaries to guard his wares and his skin to the town across the way; or the merchant bringing ore down from the mountains- he most likely does so with the permission of the Noble Houses and the Lords of Waterdeep. There are 42 recognized guilds in Waterdeep as a result from Norther economics gave the rise of seven guilds: The Horsemen’s Association, The Order, The Fellowship of Carters, Coachmen and Caravan Masters, The Surveyor’s, Map & Cryptographers Union, The Society of Lenders, Changers and Bankers, and the Fraternity of the Sword and Shield.