of the Islamic religion. His works were generally short, full of quotations from the Quran and Hadith literature, such as his main and foremost theological treatise, Kitāb at-Tawḥīd (; "The Book of Oneness"). He taught that the primary doctrine of Islam was the uniqueness and oneness of God (tawḥīd), and denounced what he held to be popular religious beliefs and practices among Muslims that he considered to be akin to heretical innovation (bidʿah) and polytheism (shirk). Wahhabism has been described as a conservative, strict, and fundamentalist branch of Sunnī Islam, with puritan views, believing in a literal interpretation of the Quran. The terms "Wahhabism" and "Salafism" are sometimes evoked interchangeably, although the designation "Wahhabi" is specifically applied to the followers of Muhammad ibn ʿAbd al-Wahhab and his reformist doctrines. The label "Wahhabi" was not claimed by his followers, who usually refer themselves as al-Muwaḥḥidūn ("affirmers of the singularity of God"), but is rather employed by Western scholars as well as his critics. Starting in the mid-1970s and 1980s, the international propagation of Salafism and Wahhabism within Sunnī Islam favored by the Kingdom of Saudi Arabia and other Arab states of the Persian Gulf has achieved what the French political scientist Gilles Kepel defined as a "preeminent position of strength in the global expression of Islam." 22 months after the September 11 attacks, when the FBI considered al-Qaeda as "the number one terrorist threat to the United States", journalist Stephen Schwartz and U.S. Senator Jon Kyl have explicitly stated during a hearing that occurred in June 2003 before the Subcommittee on Terrorism, Technology, and Homeland Security of the U.S. Senate that "Wahhabism is the source of the overwhelming majority of terrorist atrocities in today's world". As part of the global "War on Terror", Wahhabism has been accused by the European Parliament, various Western security analysts, and think tanks like the RAND Corporation, as being "a source of global terrorism". Furthermore, Wahhabism has been accused of causing disunity in the Muslim community (Ummah) and criticized for its followers' destruction of many Islamic, cultural, and historical sites associated with the early history of Islam and the first generation of Muslims (Muhammad's family and his companions) in Saudi Arabia. Contemporary Islam The contemporary period begins after 1924. With the defeat and dissolution of the Ottoman Empire (1908–1922), the Ottoman Caliphate was also abolished. This event heavily influenced Islamic thinking in general, but also what