The Imams of Yemen and later also the Kings of Yemen were religiously consecrated leaders belonging to the Zaidiyyah branch of Shia Islam. They established a blend of religious and political rule in parts of Yemen from 897. Their imamate endured under varying circumstances until the republican revolution in 1962. Zaidiyyah theology differed from Isma'ili or Twelver Shi'ites by stressing the presence of an active and visible imam as leader. The imam was expected to be knowledgeable in religious scholarship, and to prove himself a worthy headman of the community, even in battle if this was necessary. A claimant of the imamate would proclaim a "call" (da'wa), and there were not infrequently more than one claimant.