On a popular level, none of those events were immediately received in sectarian terms. Sunni groups like the Muslim Brotherhood, for example, congratulated the Shiite cleric and were even inspired by his successful establishment of an Islamic republic. The jihad in Afghanistan also focused energy on what Muslims across the region regarded as an atheist enemy threatening to uproot Islam there. But that reality would be changed, largely by one intellectual and two powerful Arab regimes.

The intellectual in question was Mohamed Surour, a Syrian math teacher who moved to Saudi Arabia in the early 1980s. A former senior member of the Muslim Brotherhood, he grew disillusioned with his organization and became influenced by the fundamentalist brand of Salafism officially practiced in Saudi Arabia. Surour was arguably the most influential religious theoretician since Sayyid Qutb, who is often dubbed as the father of modern jihadism. His legacy, of combining ideas from political Islam with Salafism, was part of a broader movement that led to the creation of the so-called Salafi-Jihadism. Two years after the Iranian revolution, he authored a book under a pseudonym titled The Turn of the Magus Has Come, a reference to the ancient Persian adherents of a religion linked to Zarathustra. The book’s core thesis is that the Shia in general, and the Iranian Shia in particular, take part in a Persian conspiracy to revive an ancient empire destroyed by Muslim conquerors in the seventh century.

Surour’s thesis was an ethno-sectarian take on Shia, which aligned with that of Saudi Arabia and Saddam Hussein’s Iraq. The two powerful Arab countries feared a revolutionary tsunami that would galvanize portions of their populations. Saudi Arabia had a sizable Shia population, concentrated in the oil-rich eastern region, and Iraq was majority Shia. In addition to the Shia threat, Saudi Arabia was already facing a growing Sunni religious movement at home, known as the Islamic Awakening, or Sahwa. Surour and his followers formed a notable part of the Sahwa movement. The book then became a key text in propagating the idea that the Iranian revolution was a doctrinal threat to Sunnis, a Trojan horse to revive the Persian empire. It received semiofficial backing by Saudi Arabia and Iraq, among others. In an interview before his death two years ago, Surour acknowledged that the text was utilized by these countries despite the fact that Saudi Arabia was at odds with his preaching, which also advocated a rejection of the religious concept of blind obedience to rulers.

In the book’s introduction, Surour captured the popular rejection of sectarianism at the time. He explained how young worshippers would push back at him as he preached on the danger of Shia. He also complained that several publishers in countries like Lebanon and Egypt threw out his manuscript after taking a glance at it. Eventually, though, his book became widely read. Such books are mostly distributed in pirated forms, but he wrote that he still sold more than 100,000 copies, a massive number by Arabic book-sale standards. The book became a key item in jihadists’ reading lists. The founder of the Islamic State, Abu Musab al-Zarqawi, for example, was reportedly an avid reader.