Guiromelans

Does anyone know much about Grazelander history/politics? I ask because the Glorantha Sourcebook says the Feathtered Horse Queen in 1623 was a somewhat scrappy piece of work called Mirina Single Matron Woman. She was so unpleasant that her own sister Vistera rebelled against her. And at one point in 1623, there were essentially two FHQs, until Mirina dies in Esrolia. Vistera becomes the sole FHQ (until she is turned into dragon poo during the Dragonrise.) So I'm wondering what kind of rebellion went on in the Grazelands? Was it a full-on civil war? Grazers killing Grazers? Clan vs clan?