First, humans in Glorantha have the same motivations as we do : recognition by others, ambition, power lust for many, greed for others. Their organisations (heortling clans, lunar empire, pent tribes, hsunchen, etc) are different from ours in that the magical/ritual element is a key part. You HAVE to depend on useful magic (gods, spirits, sorcery) to succeed. In our world, perhaps it would be ideologies that fulfill this role (or at least they did for a long time).
So the lunar noble houses use dart wars to get to the top ? Fine, look at Italy in the Renaissance, it was also common : assassinations, blackmails, economic pressures, etc. If they had had magic they would have used it. Instead they bought the Church's support and tried to have their candidate elected as Pope (they even had several Popes at some points).
In short, nothing special in Glorantha politics. Goals are very down-to-earth and magic is just a mean, like war, of furthering political aims (Clausewitz again).
Of course, this would be heresy to most priests, who sincerely and truly believe the world's order is centered on their deities. But probably not to most kings, emperors, mandarins, chieftains and khans. At least that's how I played them in Runequest. Leaders truly motivated by faith have poor results. See how Louis IX (reverred Saint-Louis) ended...
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