For almost a millennium after the Arab conquests of the seventh century, the Arabian Peninsula was not integrated into the Middle East. Although the Arab conquests began a new era in Middle Eastern history, they left Arabia drained of much of its population and relegated to a politically marginal role in early Islamic history. Later, in the Ottoman period, Egypt and the Arab Fertile Crescent became provinces of the empire, but, with the exception of peripheral areas, Arabia did not. Unlike Egypt and the Fertile Crescent states, the peninsula was governed by family and tribal elites. Islam was a crucial factor in the unification of disparate clan and tribal groups into regional confederations and kingdoms. In the imamate of Yemen and the sultanates of Oman and Saudi Arabia, religion and state were closely identified. While the shaykhs of the Persian Gulf region did not formally claim charismatic religious authority, the rulers were considered the heads of the religion, responsible for the implementation of Islamic values. Throughout the peninsula, the ʿulamaʾ, whether Zaydi, Shafiʿi, Ibadi, or Wahhabi, also played an important role as political advisors to rulers, administrators of judicial and educational institutions, and a source of moral advice and political legitimacy. Only since World War II has the peninsula become subject to the forces that have shaped the rest of the Middle East.
Yemen
Yemen has an exceptional position in the history of the Arabian Peninsula. Throughout their history, North and South Yemen had different regimes and different religious orientations. Since ancient times the south has been the center of an agricultural and state-organized society. The north has a tribal and pastoral population. Yemen was converted to Islam during the lifetime of the Prophet and was later absorbed into the early Umayyad and ʿAbbasid empires.