Muhammad's message featured violence with increasing intensity, culminating in surah 9, chronologically the last major chapter of the Quran, and its most expansively violent teaching. Throughout history, Muslim theologians have understood and taught this progression, that the message of the Quran culminates in its ninth chapter.
Surah 9 is a command to disavow all treaties with polytheists and to subjugate Jews and Christians (9.29) so that Islam may “prevail over all religions” (9.33). It is fair to wonder whether any non-Muslims in the world are immune from being attacked, subdued or assimilated under this command. Muslims must fight, according to this final chapter of the Quran, and if they do not, then their faith is called into question and they are counted among the hypocrites (9.44-45). If they do fight, they are promised one of two rewards, either spoils of war or heaven through martyrdom. Allah has made a bargain with the mujahid who obeys: Kill or be killed in battle, and paradise awaits (9.111).
Muslim thought leaders agree that the Quran promotes such violence. Maajid Nawaz, co-founder of the Quilliam Foundation in the United Kingdom, has said, “We Muslims must admit there are challenging Koranic passages that require reinterpretation today. ... Only by rejecting vacuous literalism are we able to condemn, in principle, ISIS-style slavery, beheading, lashing, amputation & other medieval practices forever (all of which are in the Quran). … Reformers either win, and get religion-neutral politics, or lose, and get ISIL-style theocracy.” In other words, Muslims must depart from the literal reading of the Quran in order to create a jihad-free Islamic world.
This is not at all to say that most Muslims are violent. The vast majority of Muslims do not live their lives based on chapter 9 of the Quran or on the books of jihad in the hadith. My point is not to question the faith of such Muslims nor to imply that radical Muslims are the true Muslims. Rather, I simply want to make clear that while ISIL may lure youth through a variety of methods, it radicalizes them primarily by urging them to follow the literal teachings of the Quran and the hadith, interpreted consistently and in light of the violent trajectory of early Islam. As long as the Islamic world focuses on its foundational texts, we will continue to see violent jihadi movements.