The Sunnis are the largest denomination in Islam, comprising about eighty five percent of all Muslims. Their difference with the minority Shia (or Shiite) Muslims arose soon after Muhammad's death, when a conflict arose over who his successor should be. The Sunnis believe that the first four caliphs--Muhammad's successors--rightfully took his place as the leaders of Muslims. They recognize the heirs of the four caliphs as legitimate religious leaders. These heirs ruled continuously in the Arab world until the break-up of the Ottoman Empire following the end of World War I.