ISIS’ Harsh Brand of Islam Is Rooted in Austere Saudi Creed By DAVID D. KIRKPATRICK

Abu Bakr al-Baghdadi, seen in an image from a video released by the Islamic State in July.Credit Agence France-Presse — Getty Images

Caliph Ibrahim, the leader of the Islamic State, appeared to come out of nowhere when he matter-of-factly proclaimed himself the ruler of all Muslims in the middle of an otherwise typical Ramadan sermon. Muslim scholars from the most moderate to the most militant all denounced him as a grandiose pretender, and the world gaped at his growing following and its vicious killings.

His ruthless creed, though, has clear roots in the 18th-century Arabian Peninsula. It was there that the Saud clan formed an alliance with the puritanical scholar Muhammed ibn Abd al-Wahhab. And as they conquered the warring tribes of the desert, his austere interpretation of Islam became the foundation of the Saudi state.

Much to Saudi Arabia’s embarrassment, the same thought has now been revived by the caliph, better known as Abu Bakr al-Baghdadi, as the foundation of the Islamic State.

“It is a kind of untamed Wahhabism,” said Bernard Haykel, a scholar at Princeton. “Wahhabism is the closest religious cognate.”

The Saudis and the rulers of other Persian Gulf states — all monarchies — are now united against the Islamic State, fearful that it might attack them from the outside or win followers within. Bahrain, Qatar, Saudi Arabia and the United Arab Emirates have all participated with Washington in its attacks on the Islamic State’s strongholds in Syria.

For their guiding principles, the leaders of the Islamic State, also known as ISIS or ISIL, are open and clear about their almost exclusive commitment to the Wahhabi movement of Sunni Islam. The group circulates images of Wahhabi religious textbooks from Saudi Arabia in the schools it controls. Videos from the group’s territory have shown Wahhabi texts plastered on the sides of an official missionary van.

This approach is at odds with the more mainstream Islamist and jihadist thinking that forms the genealogy of Al Qaeda, and it has led to a fundamentally different view of violence. Al Qaeda grew out of a radical tradition that viewed Muslim states and societies as having fallen into sinful unbelief, and embraced violence as a tool to redeem them. But the Wahhabi tradition embraced the killing of those deemed unbelievers as essential to purifying the community of the faithful.

“Violence is part of their ideology,” Professor Haykel said. “For Al Qaeda, violence is a means to an ends; for ISIS, it is an end in itself.”

The distinction is playing out in a battle of fatwas. All of the most influential jihadist theorists are criticizing the Islamic State as deviant, calling its self-proclaimed caliphate null and void and, increasingly, slamming its leaders as bloodthirsty heretics for beheading journalists and aid workers.

The upstart polemicists of the Islamic State, however, counter that its critics and even the leaders of Al Qaeda are all bad Muslims who have gone soft on the West. Even the officials and fighters of the Palestinian militant group Hamas are deemed to be “unbelievers” who might deserve punishment with beheading for agreeing to a cease-fire with Israel, one Islamic State ideologue recently declared.

“The duty of a Muslim is to carry out all of God’s orders and rulings immediately on the spot, not softly and gradually,” the scholar, Al Turki Ben-Ali, 30, said in an online forum.

The Islamic State’s sensational propaganda and videos of beheadings appear to do double duty. In addition to threatening the West, its gory bravado draws applause online and elsewhere from sympathizers, which helps the group in the competition for new recruits.

That is especially important to the Islamic State because it requires a steady flow of recruits to feed its constant battles and heavy losses against multiple enemies — the governments of Iraq and Syria, Shiite and Kurdish fighters, rival Sunni militants and now the United States Air Force.

For Al Qaeda, meanwhile, disputes with the Islamic State are an opportunity “to reposition themselves as the more rational jihadists,” said Daveed Gartenstein-Ross, a researcher at the Foundation for Defense of Democracies.

The Islamic State’s founder, Mr. Baghdadi, grafted two elements onto his Wahhabi foundations borrowed from the broader, 20th-century Islamist movements that began with the Muslim Brotherhood and ultimately produced Al Qaeda. Where Wahhabi scholars preach obedience to earthly rulers, Mr. Baghdadi adopted the call to political action against foreign domination of the Arab world that has animated the Muslim Brotherhood, Al Qaeda and other 20th-century Islamist movements.

Mr. Baghdadi also borrowed the idea of a restored caliphate. Where Wahhabism first flourished alongside the Ottoman Caliphate, the Muslim Brotherhood was founded shortly after that caliphate’s dissolution, in 1924 — an event seen across the world as a marker of Western ascent and Eastern decline. The movement’s founders took up the call for a revived caliphate as a goal of its broader anti-Western project.

These days, though, even Brotherhood members appear almost embarrassed by the term’s anachronism, emphasizing that they use caliphate as a kind of spiritual idea irrelevant to the modern world of nation-states.

“Even for Al Qaeda, the caliphate was something that was going to happen in the far distant future, before the end times,” said William McCants, a researcher on militant Islam at the Brookings Institution. The Islamic State “really moved up the timetable,” he said — to June 2014, in fact.

Adhering to Wahhabi literalism, the Islamic State disdains other Islamists who reason by analogy to adapt to changing context — including the Muslim Brotherhood; its controversial midcentury thinker Sayed Qutb; and the contemporary militants his writing later inspired, like Ayman al-Zawahri of Al Qaeda. Islamic State ideologues often deem anyone, even an Islamist, who supports an elected or secular government to be an unbeliever and subject to beheading.

“This is ‘you join us, or you are against us and we finish you,’ ” said Prof. Emad Shahin, who teaches Islam and politics at Georgetown University. “It is not Al Qaeda, but far to its right.”

Some experts note that Saudi clerics lagged long after other Muslim scholars in formally denouncing the Islamic State, and at one point even the king publicly urged them to speak out more clearly. “There is a certain mutedness in the Saudi religious establishment, which indicates it is not a slam dunk to condemn ISIS,” Professor Haykel said.

Finally, on Aug. 19, Sheikh Abdul Aziz al-Sheikh, the Saudi grand mufti, declared that “the ideas of extremism, radicalism and terrorism do not belong to Islam in any way, but are the first enemy of Islam, and Muslims are their first victims, as seen in the crimes of the so-called Islamic State and Al Qaeda.”

Al Qaeda’s ideologues have been more vehement. All insist that the promised caliphate requires a broad consensus, on behalf of Muslim scholars if not all Muslims, and not merely one man’s proclamation after a military victory.

“Will this caliphate be a sanctuary for all the oppressed and a refuge for every Muslim?” Abu Muhammad al Maqdisi, a senior jihadist scholar, recently asked in a statement on the Internet. “Or will this creation take a sword against all the Muslims who oppose it” and “nullify all the groups that do jihad in the name of God?”

Another prominent Qaeda-linked jihadist scholar, Abu Qatada al-Falistini, echoed that: “They are merciless in dealing with other jihadists. How would they deal with the poor, the weak and other people?”

Both scholars have recently been released from prison in Jordan, perhaps because the government wants to amplify their criticism of the Islamic State.