In my campaign world leaders rise to the top through all of the usual methods - force, intrigue, clever choice of parents...
But of course, with Magic being 'real' and the palpable presence of Divine power, I couldn't resist throwing in a touch of the 'Divine Right'.
I've only codified its application for one Nation so far. I imagine it works differently for other nations and/or systems of government - A Nation of Orcs might have a rather different Divine Right fueled by the will of the Orc Pantheon (hmnnnn...)
A properly constituted member of the of the Principality of Thuryn's aristocracy, who ascends to their position through duly lawful means, makes proper observances*, and who correctly and faithfully administers the law of the land is directly aided and protected by their patron's divine power.
This power is limited: Subjects are protected from the abuse of power by numerous laws and traditions, and these are actively enforced by the same powers that fuel the 'Divine Right'. A ranking aristocrat who abuses their power could easily find their powers removed, and their subjects in arms.
Powers are applied as a Template upon ascension to the title in question.
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Sovereign/Grand Duke - Currently one and the same person
DR 20/-, SR 20, +4 on Saves, Death Ward, Discern Lies (Will), Divine Favor (+4, 4/day), True Seeing (Will)
Duke - Rules a Duchy. There are currently 6 of 'em
DR 10/-, SR 10, +3 on Saves, Discern Lies (Will), Divine Favor (+3, 3/day), True Seeing (1/day)
Count - Rules a County. Typically 3 to 10 Counties per Duchy
DR5/-, SR 5, +2 on Saves, Discern Lies (3/day), Divine Favor (+2, 2/day)
Baron - Rules a Barony. Typically 4 to 12 Baronies per County
DR 2/-, +1 on Saves, Divine Favor (+1, 1/day)
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* These powers are provided through the collective agency of various Lawful (Good and Neutral) Deities within the associated Pantheon. It's actually possible to 'spoof' this to a certain degree through the agency of the Lawful Evil Deity of Tyrants, but that's a whole 'nother can o worms)
There are additional 'Peer-like' titles (Viscount, Baronet) awarded as offices not associated with ruling land - therefore not directly responsible for the lives of subjects on those lands, and thus get no special powers.
A'Mal