Business
Where power runs through families, ordinary household events become political events. A baptism, a marriage or a quarrel over inheritance can form alliances, transfer power or split factions, and so ends up shaping the life of a whole nation.
Powerful extended families both feed on a weak, corrupt state and keep it weak. Where public institutions are feeble, kin networks step in to grab state resources, and their grabbing drains those institutions further, so the two reinforce each other.
Elite families use inherited wealth and their name to get special treatment from officials. That treatment includes cheap state credit, relaxed rules, licenses for regulated businesses, and a free hand in labor disputes. In return, the families press the people who depend on them to vote for the officials who granted the favors.