An old (and tiresome) debate appears to have been settled by those best positioned to settle it.  According to Andrew Gripp, a former political science professor:

Since 9/11, one of the defining fault lines in American and Western politics has concerned whether jihadist groups such as al-Qaeda and ISIS are motivated by their religion or by politics – or more specifically, by grievances against Western foreign policy. Some insist that Islamic doctrine is the basis of their violence, while others insist that such groups are not truly Islamic, but are instead using the guise of religion to lash out against Western influence and intervention.

After indicating how "jihadist groups' political behavior is consistently traceable to their beliefs about what the Quran, hadith, and respected commentaries say they have a divine injunction to do," Gripp writes:

For years, however, making this case has been a challenge. This is in part because al-Qaeda was intentionally speaking to both sides in this debate. As the scholar Raymond Ibrahim demonstrates in The Al Qaeda Reader, the terrorist group would regularly frame its grievances in political terms when broadcasting its message to the West (so as to insinuate that once the West withdrew, peace would come). Yet when speaking to the Muslim world, the group would make highly sophisticated religious arguments, explaining why its actions, however reprehensible on their face, were in fact justified by a close reading of the holy texts.

This was indeed the main reason I sought to translate and publish al-Qaeda's internal communiqués to fellow Muslims side by side with al-Qaeda's communiqués to the West: to show the stark differences in tone and purpose.  As I wrote in the book's preface ten years ago:

This volume of translations [The Al Qaeda Reader], taken as a whole, proves once and for all that, despite the propaganda of al-Qaeda and its sympathizers, radical Islam's war with the West is not finite and limited to political grievances – real or imagined – but is existential, transcending time and space and deeply rooted in faith.

Now, however, the world need not rely on my translations and can get it straight from the horse's mouth.  In a recent article titled "Why We Hate You & Why We Fight You," the Islamic State gives six reasons.   Reason number one says it all: 

We hate you, first and foremost, because you are disbelievers; you reject the oneness of Allah – whether you realize it or not – by making partners for Him in worship, you blaspheme against Him, claiming that He has a son [Christ], you fabricate lies against His prophets and messengers, and you indulge in all manner of devilish practices. It is for this reason that we were commanded to openly declare our hatred for you and our enmity towards you. "There has already been for you an excellent example in Abraham and those with him, when they said to their people, 'Indeed, we are disassociated from you and from whatever you worship other than Allah. We have rejected you, and there has arisen, between us and you, enmity and hatred forever until you believe in Allah alone'" (Al-Mumtahanah 4 [i.e., Quran 60:4]). Furthermore, just as your disbelief is the primary reason we hate you, your disbelief is the primary reason we fight you, as we have been commanded to fight the disbelievers until they submit to the authority of Islam, either by becoming Muslims, or by paying jizyah – for those afforded this option ["People of the Book"] – and living in humiliation under the rule of the Muslims [per Quran 9:29].

This is as plain as it gets, not to mention wholly grounded in Islam's traditional worldview.  As has been repeatedly pointed out, if Muslims are persecuting their fellow countrymen – people who share their nationality, ethnicity, culture, and language – on the simple basis that they are Christians, why should there be any surprise, or excuses of "grievances," when Muslims terrorize the "infidels" of the West?

Reasons two and three of why ISIS hates and fights the West are essentially the same as reason one: Western secularists and atheists are hated and attacked for disbelieving in and living against Allah.  Although reason four cites "crimes against Islam," this is a reference to the "crime" of refusing to submit to Islam's authority and sensibilities, also known as Islam's "How Dare You?!" phenomenon.

It is only in reasons five and six that ISIS finally mentions "grievances" against Western foreign policy – only to quickly explain (emphasis added):

What's important to understand here is that although some might argue that your foreign policies are the extent of what drives our hatred, this particular reason for hating you is secondary, hence the reason we addressed it at the end of the above list. [...] The fact is, even if you were to stop bombing us, imprisoning us, torturing us, vilifying us, and usurping our lands, we would continue to hate you because our primary reason for hating you will not cease to exist until you embrace Islam. Even if you were to pay jizyah and live under the authority of Islam in humiliation, we would continue to hate you.

It is this unrelenting hatred that Westerners cannot comprehend – a hate that compels Muslim husbands to hate their non-Muslim wives and compels America's great "friends and allies" Saudi Arabia and Qatar to publish government-sanctioned decrees proclaiming their hate for America.

And it was always this hate that fueled al-Qaeda's jihad – not grievances.  All of the Quran verses that call for hate against non-Muslims have been repeatedly cited by al-Qaeda in its Arabic writings to Muslims.  (Ayman Zawahiri, al-Qaeda's current leader, wrote a 60-page treatise devoted to delineating how Islam commands Muslims to hate non-Muslims.  See "Loyalty and Enmity," The Al Qaeda Reader, p. 63-115.) 

Osama bin Laden once wrote:

As to the relationship between Muslims and infidels, this is summarized by the Most High's Word: "We renounce you. Enmity and hate shall forever reign between us – till you believe in Allah alone" [Qur'an 60:4 referenced above in ISIS's recent publication]. So there is an enmity, evidenced by fierce hostility from the heart. And this fierce hostility – that is, battle – ceases only if the infidel submits to the authority of Islam, or if his blood is forbidden from being shed [i.e., a dhimmi], or if Muslims are at that point in time weak and incapable [in which case, bin Laden later clarifies, they should dissemble (taqiyya) before the infidels by, say, insisting the conflict is about "foreign policy," nothing more]. But if the hate at any time extinguishes from the heart, this is great apostasy!… Such, then, is the basis and foundation of the relationship between the infidel and the Muslim. Battle, animosity, and hatred – directed from the Muslim to the infidel – is the foundation of our religion. (The Al Qaeda Reader, p. 43)

Yet, in every communique he issued to the West, bin Laden stressed that al-Qaeda's war was entirely based on Western foreign policies detrimental to Islam; eliminate these, and terrorism would cease.  This rhetoric was accepted at face value by many so-called "experts" (such as ex-CIA agent Michael Scheuer, author of Imperial Hubris) and became the default answer to the tired question, "why do they hate us?"  As late as 2014, U.S. President Obama invoked the "grievance" meme concerning ISIS.

It was one thing for Western leaders to accept and disseminate al-Qaeda's lies concerning "grievances" and another thing for them to continue doing so now, in light of ISIS's recent and open confessions concerning the true nature of the jihad.  Any Western leader, analyst, or "expert" who at this late hour continues peddling the "grievance" narrative falls within the ever growing ranks of fools and liars.

Raymond Ibrahim, author of The Al Qaeda Reader and Crucified Again, holds fellowships at the David Horowitz Freedom Center and the Middle East Forum.