"These heirs ruled continuously in the Arab world until the break-up of the Ottoman Empire following the end of World War I." I removed that line since it isn't accurate. Caliphates were not always heirs to the original Muslim rulers. The title of Caliph could be adopted by any Muslim rulers. The Ottoman Caliphs could not trace their lineage back to the early Caliphs since the Ottoman Empire were Turkish and settled into the lands which comprise modern day Turkey over a several hundred year period of migration. Turks and Arabs are two very different races too. Different languages, genetics, physical appearances etc.