The house that controls banking, Tamrel actually owns no major cities…but is present in every single one of them, and is actually the second richest house when compared to Raekon. To think that the family’s small land holdings betray a lack of power would be incorrect. Instead, one must realized that the Tamrel don’t care about the solid foundations of power as much as they care about power over those who own the solid foundations. Every other house is easily in Tamrel’s pocket, to an extent that they themselves may not even know, and if there is one house that would cause the most chaos by suddenly vanishing, its easily them.
In the war between Terrak, Juder, and Raekon, Tamrel stayed neutral, remaining a source of money to both, and hoping to see the end of the war with the victor(s) in their debt. This, of course, they did.