## Why is recent international (Europe, N-America, …) Islamist terrorism exclusively perpetrated by Sunnis?

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6

According to the Global Terrorism Database, the number of terrorist attacks with fatalities in Western Europe has recently started to rise for the first time since the 1970s:

Source: Global Terrorism Database

Going through the list at GTB reveals that some of those in 2015 were claimed by Islamic State (all in France):

Source: idem

Out of the remaining ones with more than one fatality, those were either also suspected salafists inspired by Islamic State, or terrorism carried out by non-muslims (such as nationalist attacks against refugee shelters or against schools).

It appears that all recent international terrorist activity by islamists in Western Europe is by Sunnis, such as those organised or inspired by Al Qaeda or Islamic State. Longer ago, Hezbollah and other Palestinian groups regularly orchestrated terrorist attacks in Europe, sometimes quite deadly (but it may be debatable whether those are accurately referred to as islamist, the motivation may rather be nationalist, such as for Palestine). Apart from the Lockerbie bombing (270 fatalities), for which responsibility was accepted by Gadhafi, attacks with more than 50 fatalities in the last 20 years were by Al Qaeda, Islamic State, or non-Muslim far-right inspired individuals (the attack listed as Greek is the bombing of TWA Flight 841 from Tel Aviv to New York, which happened to crash in Greece but Greece was not the target of the attack).

The same for attacks with 11–50 fatalities. The only Shia attack listed is the Hezbollah Al Descanso bombing in 1985:

After the Palestinian terrorist attacks in Europe died out since the 1980s, it appears the only Islamist terrorism has been from Sunni Salafi extremists.

In the above, I have focussed on data for Western Europe, but I am interested in answers either focussing on Europe, North America, or globally outside the Muslim-majority world. I have deliberately avoided data for Middle East / North Africa / Muslim-majority countries, as terrorist attacks in those are dominated by countries in warzones with a situation that is very different from Europe or North America.

Why has international Palestinian terrorist attacks ceased and is international islamist terrorism now exclusively Sunni?

(I choose the word international to exclude attacks motivated by purely domestic political motives, such as Chechen separatism or the Palestinian-Israeli conflict)

Is this strictly for Western Europe? If so, can you clarify in the OP title? – K Dog – 2017-02-06T15:39:53.697

2@KDog Although I have studied the statistics for Western Europe my interest is broader. Edited to clarify. – gerrit – 2017-02-06T15:44:34.867

8Palestinian international terrorism was mostly not "Islamist". I wouldn't be surprised if some of the Palestinian terrorists in the pre-1990s-period were actually atheists or secular... – einpoklum – 2017-02-06T22:56:21.400

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@einpoklum Valid point. Would you say a valid analogy to Palestinian nationalism and Islam would be Irish nationalism and Catholicism? On the other hand, one of prominent groups calls itself Islamic Jihad which would be fair to describe as Islamist, would it not? A group can be nationalist and communist (many 3rd world liberation movements), nationalist and islamist, nationalist and fascist, or some other combination?

– gerrit – 2017-02-07T01:14:10.053

How is it possible to determine whether any particular jihadi is Sunni or Shiite? Or are they just guessing based on national origin &c? – jamesqf – 2017-02-07T05:54:43.123

@jamesqf: If that person belongs to an avowedly Sunni or Shia Islamic organization (which organizes the attack), then it's determined. Otherwise, indeed, you can look at the Shia/Sunni distribution of his/her place of origin, but, frankly - if it's not abundantly clear then I wouldn't even try to attribute the attack to the person's religious beliefs. – einpoklum – 2017-02-07T09:30:00.897

2@gerrit: There are indeed many similarities to the Irish-vs English case: A different religion of the colonizers; a history including a period of not-genocide-but-not-incredibly-far-from it; and the fact that Irish armed groups never (to my knowledge) targeted Protestants from other countries. As for Islamic Jihad, it is: (1) very small compared to Fatah and Hamas (2) While Islamist, its goals are strictly limited to Palestine/Israel, so it's just an Islamist approach to a national struggle (3) I think they haven't carried out attacks outside of Palestine. Only 90% sure of that though. – einpoklum – 2017-02-07T09:33:47.007

@gerrit: Note also that there have been very different organizations named Islamic Jihad; and it's the Lebanese one which has seemingly carried attacks outside of Palestine.

– einpoklum – 2017-02-07T14:35:43.090

@einpoklum: But how many jihadist groups are really exclusively Sunni or Shiite? I admit I don't really understand such subtle distinctions (any more than I understand the distinctions between Christian sects), but from the outside they generally seem more interested in killing infidels than making doctrinal distinctions. – jamesqf – 2017-02-08T19:10:32.270

@jamesqf: I'd say all or almost all of them. If you're a religious organization, you're going to stick to your own, let's say, current. It's like you would not right-wing Christian organizations in, say, the US, which would be joint Catholic-Protestant. The people in such organizations tend to come from a mostly-uniform ethnic/cultural background, part of which is the religion. – einpoklum – 2017-02-08T20:19:49.613

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There are many interrelated factors, some of which are:

1. There's just a lot more Sunnis than Shia. Attacks require resources.

2. Sunnis are far better funded (KSA funding Wahhabism; coupled with Iran's relatively depleted funds due to Western sanctions). Attacks require resources.

3. Shia had other priorities (Sunnis). First you had Iran-Iraq war sapping Iran's resources; then you had Lebanon taking priority, then Syria.

And, while your question excludes "domestic motives", I'll repeat my mantra above: Attacks require resources. Palestinians' resources are targeted at attacks on (and in) Israel, so is Hezbollah.

4. Much of Shia terrorism had specific goals (your answer explicitly mentioned Palestinians) - and as two other answers expanded in detail, those goals are less of a religious and more of a geopolitical nature. Arguably, they achieved those goals to as much of an extent as pressure on the Western society could achieve, with establishment of Palestinian Authority and Oslo accords, (in many people's opinion, as a "reward" for terrorism).

This contrasts with Sunni goals, which are not fulfilled in the least (get Western influence out of Arabian peninsula and Muslim world in general; and lately, to establish Caliphate).

The former goal dovetails neatly with your timeline - Sunnis (AQ especially) had a heavy boost of grievances on the topic ever since there was heavy US presence in Kingdom of Saudi Arabia because of Saddam's 1991 adventure in oil-grabbing. OBL very explicitly called out US bases in KSA as a reason for the attacks by AQ.

5. Much of last decade, the overarching political goal was that of Sunnis - to re-establish Caliphate under the Caliph they choose.

Quoting from Wikipedia, Shia have a different take on this:

(Imam) must not be appointed by the Islamic ummah, but must be appointed by God.

6Too much of your answer is worded as though Shia muslims somehow naturally or easily tend to commit acts of terror, and circumstances are merely unfavorable right now. You also make the assumption that there are overall "Sunni goals", lumping all the Sunnis together, or even implicitly Arab Sunnis. So -1 for that. Finally, to my (admittedly limited) knowledge, the Oslo process and the establishment of the PA was not an actual goal and is not perceived as a solution to the Palestinian problem in a way which would significantly reduce hostility towards Israel or the US. References please? – einpoklum – 2017-02-06T22:19:34.217

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-1 if I could (I don't have the rep). "Shia had other priorities (Sunnis). First you had Iran-Iraq war"? You make it sound like Iran (Shia) was the aggressor here, whereas may I point out that it was Iraq (Sunni) who invaded Iran (Shiite)? I'm not even sure what part of that falls under terrorism (and hence is at all relevant) given it was an actual war...

– user541686 – 2017-02-07T07:07:28.400

3@Mehrdad - as far as I recall, Iraq was the aggressor, yes - the answer wasn't meant to imply otherwise. However, it doesn't matter who's the aggressor, if you're fighting a war, you're fighting a war and your resources are devoted to that either way. An actual war actually takes MORE resources than proxy terrorist attacks. – user4012 – 2017-02-07T11:40:59.990

2Yes, and my point is, if you're talking about the war, then you're not answering the question, which was about terrorist attacks, not wars. – user541686 – 2017-02-07T12:06:34.750

4@Mehrdad And the given answer was that they were too busy dealing with a war to have time for supporting terrorism. That may or may not be a good answer but it's certainly an answer. – David Richerby – 2017-02-07T12:43:21.983

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The answer by user4012 is pretty good. I do agree that, while some of the stated religious doctrine may still seem a bit extreme to our western sensibilities, most of the Shia-sponsored terrorism had more traditional political aims, ultimately.

A lot of what Al-Qaeda used to do, and what ISIS does now falls into the ideological doctrine of Wahhabism. As user4012 pointed out, this brand of extremism, which doesn't have political goals that fall into more established political boundaries (literal national boundaries), saw decades of high-amount and high-level funding from the Saudis, primarily, to build up to this point.

What sets this kind of extremism apart is the belief that not only are other "brands" of Islam wrong, but they are evil, and must be converted or purged. They are, literally, at war with any non-extremist elements within Islam, as well as outsiders to the religion.

The main government sponsors of Shia extremism or terrorist actions - Iran and Syria, are within the traditional city-state structure, so they are a bit more pragmatic in how they want their support to be directed, because they have their own nations at risk. ISIS doesn't have these kinds of borders and their backers aren't as formally and overtly state-tied to the movement.

A couple more factors that impact are that they have achieved a certain amount of success, with Hezbollah recognized as an actual political player in Palestine, but, more importantly, there is the factor of the extremist group ISIS essentially being at war with Shia Islam, with the goal of stomping them out like everyone else.

Many of their resources are now directed at fighting ISIS, which is why we have the odd bedfellows of Iran being the main supplier of direct military force with the USA while the USA stepped back to re-boot the attempts to train-up the Iraqi military, and the USA and NATO trying to work with Russia and Russia-backed Syria in hitting ISIS while trying to prevent them from "accidentally" hitting the elements we are supporting that look to topple Assad.

(Since I'm at work, I can't do extensive searching for all the links to back this up. I will return and edit with citations, later today)

Why does everybody keep mentioning Wahhabism, when it's not actually a thing? You're talking about the rejectionists, khawaarij – aross – 2017-02-07T13:44:00.620

1@aross - That's absurd. Of course it's actually a thing. People describe ISIS as similar to the Khawaarij, but their underlying philosophy is driven by Wahabbism, which is and has been a real thing. – PoloHoleSet – 2017-02-07T14:12:13.950

Well, what actually is it? I don't generally take my religious courses on Wikipedia, but even wiki is not decisive about it. Since Wahhabism (referring to one of Allah's names!) does not mean anything negative, it should be considered odd that nobody (not of any significance anyway) ascribes themselves to it. – aross – 2017-02-07T14:18:13.323

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Wahhabism specifically refers to a defined sect that follows specific tenants. The ROOTS of the term may come from one of Allah's name, but Wahabism is some that is specifically defined. Here's an explanation from a Muslim advocacy and support group. If you want to call them up and tell them they don't know what they're talking about, feel free -

– PoloHoleSet – 2017-02-07T14:22:27.677

@aross - "what is it?" There are books about it, so don't expect something exhaustive. Wahhabists believe in a very strict, literal interpretation or the Koran, believe anyone who doesn't follow their exact doctrine are heathens and enemies, and believe that they are tasked with trying to bring about a united Islamic state/caliphate, to dumb it down quite a bit. They're similar to fundamentalist Evangelical Christians (especially the young Earth creationists) in their adherence to a rigid, literalist, doctrinaire ideology. – PoloHoleSet – 2017-02-07T14:27:48.600

So now it's clear your coming from s sufi POV: http://www.islamicsupremecouncil.org/understanding-islam/spirituality/2-the-sufis-enlightened-community-builders.html Which shouldn't be surprising, as shaikh abdulwahhaab opposed many sufi practices such as intercession at graves

– aross – 2017-02-07T14:44:58.550

2@aross - nope, that's a characterization of convenience for you. I never heard of them, ever, before coming across that link. I don't have a specific point of view on this, other than it's clear that your claim that it is "not a thing" has zero fundation. There were literally tens of thousands of links talking about this thing you claim doesn't exist that I could have chosen from. Do the Google thing and take your pick. To claim something doesn't exist that is this well established and recognized across cultures, and any other kind of dividing line you can come up with, is absurd. – PoloHoleSet – 2017-02-07T15:20:03.943

Since you didn't even know what Sufism is, I don't think your opinion has any value. It was actually the sufis who invented the term "Wahhabi" and applied it (as defamation) to anyone who dared oppose their practices of calling upon dead people in their graves (which clearly contradict Islamic monotheism). So the sources you will find are mostly Sufi (many Shia also adopted it). So not you, but your sources are from a Sufi POV. And about the naming controversy, here you go: https://en.wikipedia.org/wiki/Wahhabism#Naming_controversy:_Wahhabis.2C_Muwahhidun.2C_and_Salafis

– aross – 2017-02-07T15:33:14.303

@aross - Not sure why it matters that sufis invented the term, it is widely used and accepted and has a specific definition. That makes it an actual "thing." Look at ANY Islamic site, at the thousands of books and articles by policy experts and Islamic scholars, and you'll see recognition and discussion about it. Not sure why you think you magically have more credibility than the rest of the planet, but, again, your premise is completely idiotic. Not sure why you think your opinion, in the face of the rest of humanity, has any value. Thanks for playing. – PoloHoleSet – 2017-02-07T15:40:54.297

You are cherry picking. Wikipedia has an entire paragraph about the naming controversy (and YES, lots was written about that controversy as well, including many scholars arguing the term shouldn't be used). You can pretend it doesn't exist... – aross – 2017-02-07T15:46:01.120

– PoloHoleSet – 2017-02-07T15:57:48.353

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## TL:DR

Because Iran has shifted away from terrorism in Western Europe to terrorism, money laundering, and narco-trafficking in Latin and South America, and for proxy wars against the West and Sunnis in the Middle East. In short, it no longer needed to travel to Europe to strike Westerners. It could do so in Iraq, Yemen, and Afghanistan.

For example, Iran blew up the AMIA building in Argentina killing some 85 people in just one event. That would have spiked your results.

In related bombings:

The bombing came two years after the 17 March 1992 bombing of the Israeli Embassy in Buenos Aires which killed 29 and wounded 242, and was Argentina's deadliest attack until the AMIA bombing. The Islamic Jihad Organization, which according to Robert Baer operates under the umbrella of Hezbollah and is linked to Iran,[17] claimed responsibility for that bombing.[18] Some[who?] suspect that the AMIA bombing was connected to the embassy attack.[19] To date, authorities have been unable to locate those responsible for either of the two bombings.

The day after the AMIA attack, a suicide bombing on a Panamanian commuter plane killed all 21 passengers, 12 of whom were Jews. Investigators determined that the bombing was perpetrated by a "Lya Jamal" – thought to be "an Arab traveling under an alias, using fraudulently obtained Colombian documents."[20] Eight days after the AMIA attack, the Israeli embassy in London was car-bombed, and thirteen hours later a similar car bomb exploded outside a Jewish community centre in London. No one was killed but 22 were injured and "millions of pounds of damage" was done.[21] Five Palestinians were later arrested in London and two convicted and sentenced to 20 years in prison in connection with the bombings

This type of evidence seems counter to your general thesis about Iranian and Palestinian bombings.

South American drug trafficking and terrorism

On March 18,[2015] the House Subcommittee on the Middle East and North Africa and the Subcommittee on the Western Hemisphere held a joint hearing about Iran and Hezbollah’s involvement in Central and South America. The committees discussed Iran's attempts to expand its influence in Latin America during the last 30 years, as well as the *Islamic Republic's alleged involvement in attacks in Peru and Uruguay and the mysterious death of Argentine prosecutor Alberto Nisman.

...

“Iran and Hezbollah’s history of involvement in the Western Hemisphere has long been a source of concern for the United States. Given the nature of transnational criminal networks existing in Latin America and the rise of terrorism ideology being exported worldwide from Middle East, it is disturbing that the State Department has failed to fully allocate necessary resources and attention to properly address this potential threat to our nation. It is well known that Iran poses a security threat to regional affairs and has expanded its ties in countries such as Cuba, Venezuela, Nicaragua, Argentina, Bolivia, Brazil, and Ecuador. The United States needs a comprehensive understanding of Tehran’s efforts in Latin America in order to thwart any potential risk to our allies and U.S. national security.”

And from the HuffPo

Iran’s increased engagement with its South American allies is one way Tehran can get around the raft of economic and diplomatic sanctions imposed by the United States and its allies.

Hamas and Hezbollah have also leveraged its connections to narcotraffickers and other transnational crime syndicates in the region to raise money for future terror operations, Southern Command chief Gen. Douglas Fraser told Congress in March.

“We do see evidence of international terrorist groups benefitting from ... illicit trafficking and money laundering” in South America, he said in written testimony during a March 13 Senate Armed Services Committee hearing.  Specifically, both Iranian-backed terror groups look regularly to South America to finance their operations in the Middle East, Frasier said at the time.

Iranian involvement in Iraq, Afghanistan and Yemen

In Iraq, Iran partnered with Sadr and the Madhi army to fight Sunnis and the US. See link

Yet Iran's policies toward Afghanistan are linked to its fierce strategic competition with the United States for a dominant role in the Islamic world.

Having gained strategic depth in Afghanistan, Iran has developed asymmetrical capability to disrupt U.S. operations or retaliate against American troops, should Iran's nuclear facilities be attacked.

Iran has called on foreign forces to leave Afghanistan, and has reportedly provided limited military support to anti-American forces as the Taliban.

Finally Yemen:

Yemen has mostly fallen to Iranian proxies--the Houthis--where it has repeatedly struck out at the US, for example the US Marines disarmament situation and firing on US Naval ships:

The toppling of the Yemeni government by Iranian backed Shi’ite Houthis has upped the ante in the regional sectarian Sunni-Shi’ite struggle.

Yemen is perfectly set to become a sectarian war that will see millions more in foreign funds transferred to various proxy forces in the country, as in the case of the ongoing civil war in Syria.

Do you think Iran was/is so influential that a change in policy in Iran is enough to explain the shift? – gerrit – 2017-02-06T16:08:56.797

@gerrit Sorry, but not following. Can you elaborate? – K Dog – 2017-02-06T16:11:20.377

Change in policy by whom and what shift exactly? – K Dog – 2017-02-06T16:14:22.567

@gerrit - Iran underwrites (money and training and diplomatic cover etc...) most of Shia groups (definitely both Hezbollah and Palestinian ones). He who pays the money, gets to order the music. – user4012 – 2017-02-06T16:14:42.407

@KDog I mean, do you think change in behaviour by the government of Iran is sufficient to explain the now absence in Shia terrorism in Europe (as opposed to the 1970s-1980s)? I find it difficult to determine how large the influence of donors on terrorism really is, in particular since some forms of terrorism are very low cost (think Nice lorry attack, or a shooting in a country where firearms are easy to obtain). Perhaps that is a different question. But probably one that is too broad. – gerrit – 2017-02-06T16:29:25.773

3@gerrit I think the important thing to note about Iran is that it's a state sponsor of terrorism. While you have some rogues out there (see the UNC truck attack, e.g.) the Iranians don't really freelance. When they blow up buildings in Argentina or use the Houthis to topple Yemen, or support Hezbollah in Lebanon and Syria they have very specific state aims. Given the US Iraq war, incursions into Afghanistan, the Syria Civil War, their own sanctions, Yemen, they have a target rich situation that needs immediate attention of their time and resources. They have no time for Europe right now – K Dog – 2017-02-06T16:38:48.593

https://en.wikipedia.org/wiki/AMIA_bombing – K Dog – 2017-02-06T16:40:44.127

@gerrit please see revised intro – K Dog – 2017-02-06T16:48:23.390

@KDog Wasn't aware of the AMIA bombing but that one too is over 20 years ago, only slightly more recent than the wave of Palestinian airline hostage-takings from before I was even born. – gerrit – 2017-02-06T16:54:31.773

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-1 for suggesting that Iran has an agenda of "striking Westerners" in Iraq, Yemen and Afghanistan. First, Westerners live in the West, not in those countries, except for small numbers of expats which I don't even believe you meant (and are certainly not struck by Iran); second, Iran has been cooperating with the US with regard to the situation in Iraq for quite a few years (as far as the US sharing a base with an Irani-backed militia for example); third, ...

– einpoklum – 2017-02-06T22:11:09.507

1... third, to the extent that you mean striking US soldiers, that does not happen in Iraq, in which the Irani-backed militias are cooperating with the US military (perhaps unfortunately), not in Afghanistan where the US is fighting local militias on the basis of resisting the occupation and/or Sunni muslim inspirations and infuences, and not in Yemen where there are also no Iranian forces. Now it's true that Iran supports the Hawthi rebels to some extent, but if anyone has been striking anyone, it's the US and Saudi Arabia pounding rebel-held areas rather than the other way around. – einpoklum – 2017-02-06T22:14:55.617

4@einpoklum Right in the article you post it states: Some of the Iran-backed Shiite militias at the base have killed American soldiers in the past. Sheesh. How many times did Khomeni today call the US the Great Satan? – K Dog – 2017-02-06T22:21:11.050

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@KDog: Apparently you can have a "bromance" with the Great Satan's secretary of state; you can write personal letters to the head of the Great Satan; and so on.

– einpoklum – 2017-02-06T22:54:36.867

4@KDog How many times did Khomeni today call the US the Great Satan, every time he needed to fire up domestic support, perhaps. Maybe even more often than Bush has referred to Iran as the axis of evil. – gerrit – 2017-02-07T13:01:19.247

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Why has international Palestinian terrorist attacks ceased?

This has several reasons; they're not distinct from each other; and I will not list them in order of importance necessarily. Nor will I list them all.

First note that Palestinian terrorism is not in essence, and often not in form, "Islamist". It's rooted in a struggle against occupation and colonization. So even if part of the resistance to those occupation and colonization is by Islamic movements or forces, and even if there are religious overtones to some of the terror attacks by Palestinians, it's not actually about religion. This fact also explains why changes in the situation of the Palestinians politically/nationally changed the nature, location and frequency of the use of terror (regardless of your definition of what it constitutes), despite the fact that religiously, not much of significance has happened.

But to be more concrete, an important reason for the drop in terror attacks by Palestinians is that Palestinian political movements - at least their military wings but not just those - have been driven out or have left, partially or wholly, centers of activity outside of Palestine; most prominently, Jordan in 1970 and Lebanon in 1982 etc. They have moved or shifted their focus of activity into the 1967-occupied parts of Palestine. This is true first and foremost for the Fatah movement, and the PLO as an organization. It reflects on what kinds of activities they initiate and where. Before, they could mostly confront the occupiers on the (effective) borders of the Israeli state, or abroad. And abroad they could either stage feeble protests (I'm exaggerating here) or use armed actions - plane kidnappings, revenge assassinations etc. In Palestine itself the spectrum of activities, both unarmed and unarmed, is much wider, arguably more effective, and obviously more captivating of focus than trying to terrorize Israeli officials abroad.

There is also the Imeprialist-orchestrated proces of pacification and political dialog - the "Peace Process" as many refer to it. When you parley, you don't strike; or at least, not as much. Of course, not all political movements have been involved in this process - with the prominent example being Hamas, currently the ruling party (*). It was actually responsible for the vast majority of armed attacks against Israelis during the 1990s, the years of the Oslo accords and their gradual implementation until they either broke down or reached their necessary dead end. After that, parts of Fatah resumed armed activity as well (and this includes both actions against soldiers and against civilians). During the early 2000s, you had no parley and lots of attacks. But all these and subsequent changes are mostly within Palestine, not in the west.

A final reason is that we seem to have had be a sort of zeitgeist change from the 1960s and 1970s into the 1980s and later. Somehow people were under the impression that radical change was just around the corner, or potentially just around the corner, and some decisive actions could bring it about relatively quickly if not easily. That also seems to have changed in 1980s - although it had been rekindled in the Arab East in 2010-2011. But - not in Palestine, or not for Palestinians.

(*) - They won the last elections; the fact that a US- and Israel-backed coup attempted worked for them in the west bank doesn't change that. I don't support them one bit, by the way.

And is international islamist terrorism now exclusively Sunni?

As others have noted, there are not-so-many Shia but lots of Sunnis. There's an even lower Shia-to-Sunni ratio, I believe, among people visiting or living in the West. So it would be quite anomalous for there to be many Shia attackers.

Also, the US is quite busy waging war in multiple Sunni-majority countries, and it's been that way for, what, over 15 years straight. Now, you do have Iraq, but after occupation a Shia or Shia-oriented government was installed, and IIRC the US remained militarily active more against Sunni(ish) elements there. The US has not attacked Iran, and has not managed / not tried to organize any sort of coup since the 1950s, so despite Iranians likely not being very fond of the US (justly or less so), I would not expect any of them to look forward to attacking it. Even more so with Europe with which Iran has nearly ok-ish relations.

PS - Note that some attacks, particularly some attacks attributed to Shia (or to Shia entities like Iran) are not necessarily proven to have been carried out by them. For example, the 1994 AIMA bombing in Argentina has a rather bizarre history of intrigue surrounding its investigation; the supposed motivation for the bombing for Iran doesn't square very well with preceding events; and no trial has been held nor any person convicted (although I think that's probably due to the implicated people not being around).

0

I disagree with most of what other answers say till now.

It is because of differences in ideology.
Based on Shia ideology:

• Shia follows their Marja s. They can not act self-willed. Marja s are top cleric shia scholars. If a Shia Muslim kill a person without permission of a Marja, Shia dont recognize him/her an standard Shia.

• Killing Human is Haram, i.e. unlawful, unless in special conditions (In fact even killing animals is abominable, with some exceptions. Even Removing leaf of tree without reason, dosent recommended)

• Defense: include self-defense and defending all Muslims (Shia and Sunni). for the second case there is an Exception: If the leader has a peace treaty with a group of infidels, then he must adhere to the treaty. For example, Iran supply Hezbollah (which is Shia) and Hamas (which is Sunni) against Israel, because Iran consider Israel as occupier of Muslim lands and murderer of them. On the other hand Iran dont intervene Russia-Chechen problems, because Iran has peace treaty with Russia.
• War with Imams of kufr, i.e. Those who have all of the following properties "infidels, leading and spreading infidelity, and dont adhere treaties".

As a result a Shia can not do a suicide bombing at a place that there are civilians, and consider this action as an Islamic action. If do, (s)he would go to hell in the hereafter.

Note:
It is not the case that all Sunni Muslims accept terrorist attacks like what Daesh do. Even It is not the case that all Salafists accept terrorist attacks like what Daesh do.

Salafists have branches. The worst of them (which include Al-Qaeda and Deash) are Takfiri Salafists, supported by Wahhabi king of Saudi Arabia. Takfiri Salafists know all people of the world (of course except themselves), including Shia Muslims and majority of Sunni Muslims as infidels and enemies.
Another group of Salafists are Jihadists. The difference of Jihadists and Takfiries is that, Jihadists dont accept the idea of Takfiries that say Kill them all. But they believe at war with e.g. Israel.

1

How about the AMIA bombing or Palestinian hostage-takings in the 1970s-1980s?

– gerrit – 2017-02-07T10:49:35.887

1- It is not proved to done by Iran, and i personally dont believe Iran is responsible for it. 2- As i said "If a Shia Muslim kill a person without permission of a Marja, Shia dont recognize him/her an standard Shia." So it is possible that a perverse Shia to do So. As you see a perverse Christian kill thousands by a single Bomb, though Jesus (PBUH) forbid from such actions. – user 1 – 2017-02-07T11:36:50.403

1I was not aware of the difference between Jihadists and Takfiris. – gerrit – 2017-02-07T12:54:50.353

+1 for suggesting that some/all/most attacks attributed to Shi'a muslims are not necessarily established facts. However, I think the claim your claim/suggestion that Shia are essentially incapable of initiating a terror attack is invalid in my opinion. After all, you can use the "self-defence of all Muslims" argument to justify almost anything you do. – einpoklum – 2017-02-07T14:00:20.870

@gerrit: "Mujtahed" - literally someone who makes an effort, undertakes an ordeal ("Jihadi" - a person associated with Jihad). "Takfiri" - a perfson associated with "Takfir", who engages in "Takfir". And what's "Takfir"? The proclamation/singling-out/focusing on "kufr", blasphemy. – einpoklum – 2017-02-07T14:02:22.043

@einpoklum About your statement "you can use the "self-defense of all Muslims" argument to justify almost anything you do": 1- I can not imagine that one can justify killing civilians in France, Iraq, Syria,... as self-defense. 2- when a person kill civilian with Suicide belt, He kill himself too. He know that God see and there is no Opportunity to repent. So it is not matter of justification. one must be Sure. If his action lacks Sharia permission, He will be punished for killing both himself and others – user 1 – 2017-02-07T15:38:25.563

"The difference of Jihadists and Takfiries is that, Jihadists dont accept the idea of Takfiries that say Kill them all. But they believe at war with e.g. Israel." I don't understand this statement, can you reword or elaborate? – TaterJuice – 2017-02-07T16:39:34.013

(1) I can imagine it very well, as I've heard "my attack is part of group self-defense" arguments many times to justify all sorts of things (not from Shia Muslims though, but I have met very few of them). Think "deterrance". (2) Not much difference between the two, effectively. If you can justify something, it's not inconceivable that you can actually believe it to be true. Now, as for punishment - perhaps you're right, but that will happen after-the-fact. – einpoklum – 2017-02-07T16:52:02.660