"The rapid formation of the Almohad hierarchy was made easier by the fact that there were pre-existing mechanisms and traditions for forming larger alliances within the tribes themselves. Alliances were based on power. Depending on the strength of the sheikh or tribal chief, some tribes were stronger than others. Not all tribes were purely isolationist in nature. Intermarriage and a confluence of tribal identities probably produced a vague sense of Masmuda identity even before the rise of Ibn Tumart. Ibn Tumart used a combination of military action, co-option of tribal traditions and tribal leaders, and persuasive indoctrination to transform this vague sense of unity into a solid government and army."
Incidentally, Fromherz is the author of a biography of Ibn Khaldun that just came out in paperback.