Over the previous decade, Islamic State were involved in a lot of terrorist attacks on the West, especially Europe, e.g. just finding ways to kill large numbers of civilians.

But if their goal was to establish their own caliphate, why did they expect this to work? Was it to try to intimidate western forces into leaving the Middle East? But surely they would have known - as recent history has shown - that the West would not simply go home because of a few civilian attacks - if anything it would make them come down harder! The response to 9/11, for example, should make this obvious. I find it hard to believe that such a well organised group would make such a basic mistake.

Also, the major occupying powers in the Middle East were USA, UK and Russia - but many of the attacks were in countries like Belgium and France.

  • Have you any evidence that the attacks did make the populations of European countries more pro-war, or did they increase anti-war sentiment?
    – Stuart F
    Oct 5 at 20:10

The involvement of ISIS in terrorist attacks on the West is actually more limited than one might expect.

Especially when excluding those attacks that weren't planned by ISIS, but "only" inspired by them, they mostly focused their terror attacks on the middle east (see also this map; this approach differentiates them from eg Al Qaeda).

Of the attacks in the west, you eg have the November 2015 Paris attacks - which ISIS claims was in retaliation to French airstrikes - and the 2016 Brussel bombings (with similar reasons given).

Apart from ISIS claimed reasons, further reasons can include:

  • "ensur[ing] [...] allegiance through fear and intimidation" (targeted at people living in or near territories ISIS controls)
  • "intimidate civilian populations", force governments to "make rash decisions"
  • "mobilise its supporters"
  • "polarise by driving Muslim populations – particularly in the West – away from their governments" / "Eliminate neutral parties through either absorption or elimination"
  • "bolster morale" and "distract attention from its loss of territory"

It's extremely difficult to get into the specific motivations of individual actors or even organizations, absent explicit statements - which are often of questionable credibility if the speaker knows their statement will be available to public scrutiny.

This thesis lays out a review of the relevant literature on the matter, and identifies five main objectives that terrorist organizations in general have as a motivation behind their tactics:

  1. Attrition - Infliction of unbearable losses on a given enemy in order to compel them to make concessions.
  2. Intimidation - Controlling public behavior of large populations by demonstrating the capacity to inflict harm in response to non-compliance. This is more often used locally, within their area of control, rather than as an attack against foreign soil.
  3. Provocation - Goading an enemy into retaliation, ideally disproportionate and indiscriminate retaliation which serves to increase sentiment against the enemy, creating a pipeline of potential recruits for radicalization.
  4. Outbidding - As with intimidation, this strategic method is largely aimed at local populations and involves a sort of 'counting coup' effect wherein demonstrating power to strike at rivals helps to establish legitimacy of the organization in the eyes of a population whose support they desire.
  5. Spoiling - Terrorist organizations that are able to operate despite ongoing negotiations or agreements with ostensible 'legitimate' governments (in ISIS' case, the Afghan national government or Republic of Iraq), undermines such agreements or negotiations by reducing the de facto legitimacy of the actors at the negotiating table; if they can't wrangle the terrorist organization, how can they be seen as credible power brokers in the region?

Goals such as vengeance or reduction of fighting capability (the latter of which is arguably not an act of terrorism so much as it is an act of war), tend to be short-run and thus not within the academic meaning of 'strategy' but for common language use cases they could be viewed as part of the strategic landscape.

  • 3
    I'd argue 3 is the most important point here. Referring to OP's question, sure the western response to 9/11 was aggressive (some would say murderous...), but it was great for recruitment into these terrorist groups. It's even what ultimately spawned ISIS!
    – llama
    Oct 5 at 18:55

They were at the time losing the open war in Syria. The terrorist attacks drew away attention from those losses. Map of IS-controlled territories by the BBC:

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This is a more complex question than one might realize. The modern political world (since the early 20th century) has been marked by a dramatic increase in the power and efficiency of national military and police forces, both in terms of military hardware and surveillance capabilities. This has pushed counter-national movements to organize as partisan forces: loose, decentralized, and lightly organized groups and individuals working for the common purpose of opposing organized regimes. We have a lot of terms for that these days: terrorist cells, lone-wolf actors, radicalized individuals, etc., but the common theme is that any movement of this sort is going to have a wide, diffuse, largely non-coordinated assortment of individuals who follow the movement's lead and principles while having only minimal contact with the movement itself.

ISIS was unique in that it had the ambition to establish a new state of its own (not merely terrorizing, subverting, or taking over some established state), but it still had a far-flung net of partisans who largely agreed with its intention without any effective connection with the more organized core of people working militarily in the Middle East. It's an interesting but difficult question whether the actions of these partisans can properly be attributed to ISIS; certainly they can be attributed to the broad movement, but not necessarily to those groups busy trying to establish a Caliphate through normal military means.

As a general rule, only the weakest and most disempowered groups undertake terrorism, because striking at 'soft' targets from hiding is the only way they can exert influence. The more power a group obtains, the more inclined they are to organize and assert their power directly, the more concerned they become with reputation and legitimacy, and the less they want to be associated with mindless, non-directed violence. ISIS at its height was an effective military force with pretensions of being a full-fledged state; terrorism would not have been in its best interests. But partisan actors are notoriously difficult to control since they act from ideology, not pragmatic concerns.


I once read that one of the goals of the terrorist attacks is to make Muslim minorities in Western countries feel hostile and not welcome in their environment. To some extent, they want to provoke people in Western countries (with different beliefs or no beliefs at all) to perform hate crimes against Muslim minorities as an act of revenge. By turning into scapegoats, these minorities in turn start to despise "the others", the ones that oppress them or even worse - the whole society they're living in, in case a large amount of people falls for that. This might lead to them supporting the cause of ISIS, both ideologically but also by moving back to Muslim countries in attempts to "unmake" the diaspora. Also, by nurturing this hatred it's easier to radicalise people already live within potential target countries, so all in all, these kind of attacks potentially supports their larger cause in several aspects, not just in "killing infidels".

Even though it's not the article I once read, I found a source backing this up:

“This is precisely what ISIS was aiming for — to provoke communities to commit actions against Muslims,” said Arie Kruglanski, a professor of psychology at the University of Maryland who studies how people become terrorists. “Then ISIS will be able to say, ‘I told you so. These are your enemies, and the enemies of Islam.’”



As an aspiring political scientist, the answer is rather disheartening. A policy to "never negotiate with terrorists" actually benefits the terrorists. The reason is simple: when no terrorists are negotiated with, a "pooling equilibrium" is created that throws all of the soft-liners in with the hard-liners. This happens because the people who otherwise could be ameliorated through negotiations are no longer able to get anything by going to the table and thus start acting like terrorists. If the hard-liners want to grow their ranks, they can simply attack the "we-do-not-negotiate-with-terrorist" countries and, in the ensuring assault on the hardliner's home territory, get a bunch of soft-liners to move toward the hard-liners.

The proof of this is in Bruce Bueno de Mesquita's Principles of International Politics textbook, chapter 13. It models the above situation as a continuous game with Bayesian updating to inform the priors. It's also a great introductory problem to a real-world application of Bayesian methods in modeling state behavior.

  • Welcome to Politics! Can you elaborate a bit more how this applies to ISIS in practice? Can you show for example that soft-liners joined ISIS rather than fleeing the country or joining some other movement with a less radical approach?
    – JJJ
    Oct 7 at 19:25
  • Well this isn't a formal analysis, so take it with a few (big) grains of salt, but imagine that a village in the Levant is destroyed. If there's nowhere to either internally or externally migrate too, and ISIS is a still-standing, stronger hand in that region, they might be the best option for the members of that community to pledge loyalty to. The members of that community may not want to join but with no outside options are forced to. This is definitely a "very far away and squinting" approach to this particular problem. A better example, the one cited in the textbook, is Hamas in the ME. Oct 8 at 16:31

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