KNOWING YOUR ENEMIES:

Three scholars, in particular, have had an outsized influence on Islamic State's religious ideology.

The first dates back to the 13th century, a period when Islam's early empires began to decline after five centuries of expansion. As the Mongols swept across Asia and sacked Baghdad, the Mongol warrior Hulagu, a grandson of Genghis Khan, threatened to overrun the Levant, an area of the eastern Mediterranean centered around modern-day Syria and Lebanon. While many Muslim scholars at the time lined up to support the Mongols, one jurist forcefully rejected the invaders. Ibn Taymiyya, an Islamic scholar from Damascus, issued several fatwas (religious rulings) against the Mongols -- and al Qaeda, Islamic State and other militants still quote those rulings today.

After Hulagu, some Mongol leaders nominally converted to Islam, but Ibn Taymiyya considered them infidels. He also argued that it was permissible for believers to kill other Muslims during battle, if those Muslims were fighting alongside the Mongols. Ibn Taymiyya is the intellectual forefather to many modern-day Islamic militants who use his anti-Mongol fatwas -- along with his rulings against Shi'ites and other Muslim minorities -- to justify violence against civilians, including fellow Muslims, or to declare them infidels, using the concept of takfir. Islamic State often quotes Ibn Taymiyya in its Arabic tracts, and occasionally in its English-language propaganda, as it did in its magazine, Dabiq, in September 2014.

Ibn Taymiyya also inspired the father of the Wahhabi strain of Islam that is dominant in Saudi Arabia today, the 18th century cleric Muhammad ibn Abd al-Wahhab, who decreed that many Muslims had abandoned the practices of their ancestors. Wahhab believed Islamic theology had been corrupted by philosophy and mysticism. Many of the practices he banned were related to Sufism and Shi'ism, two forms of Islam he particularly abhorred.

Wahhab argued that Islamic law should be based on a literal interpretation of only two sources: the Koran and the Sunnah, a collection of the Prophet Muhammad's sayings and stories about his life. (The word Sunnah means path, and it's the root of the designation "Sunni" -- those who follow the prophet's path -- the dominant sect in Islam.) Wahhab dismissed analogical reasoning and the consensus of scholars, two other sources that had helped Islamic law evolve and adapt to new realities over time.

Today, Saudi Arabia is built on an alliance between two powers: the ruling House of Saud and clerics who espouse Wahhabi doctrine.

Tweet   @brothersjudd