The bigger goal, the central Islamic goal is, of course, to bring non-Muslims under the rule of Islamic law. That goal is laid out clearly and unmistakably in standard Islamic doctrine. But why does ISIS think that randomly blowing up and shooting infidels will achieve this?
The strategy ISIS and other orthodox Muslims are now following was laid out by by the late Sheikh Abu-Bakr Naji. His big insight was this: It is impossible now to achieve Islam's prime directive the traditional way, which was to invade countries and establish Islamic law by force. This method may have worked fine when non-Muslim countries were unconcerned with things happening in other parts of the world. Back in those days, using the traditional method, Islam successfully established most of the now-existing 56 Muslim countries. But these days non-Muslim countries are too powerful militarily and would stop it. Naji thought the Taliban did a great job setting up a true Islamic state, faithful to Islamic law, but look what happened: The "crusader nations" destroyed it.
Osama bin Laden thought he would make the cowardly infidels succumb to fear with a few very big violent attacks, such as 9/11. But that strategy failed. It only strengthened non-Muslim resolve and triggered a massive retaliation.
So in 2005, Naji proposed a new strategy: He said the way to ultimately accomplish the prime directive is to fight the entire non-Muslim world everywhere at once, and to create an increasing occurrence of ever-more-violent events so non-Muslims everywhere would feel insecure and would eventually live in constant fear of violent death. They would lose trust in their government's ability to protect them. They would become exhausted from insecurity and fear, and would then be willing to embrace Islamic rule just to make the violence stop and to be able to live in some sort of peace.
I just read an article about the Friday 13th attack in Paris, and the New York Times quoted a 42 year-old French accountant: "I feel sickened, angry," he said. Coming so soon after the attacks in January, he said, "It is starting to be too much." This struck me as an expression of exactly the state of mind Naji was talking about.
In order to accomplish frequent attacks, Naji said Muslims must create bases of operations inside the non-Muslim nations. That means Muslim immigration is necessary, coupled with the Muslims' refusal to integrate into the non-Muslim society, leaving areas of Muslim-only populations (what many have called no-go zones) within non-Muslim countries. This way, terrorism operations could be organized and carried out more effectively.
ISIS and other Islamic groups have embraced this strategy worldwide.
Muslim immigration into non-Muslim countries has increased, especially with the new influx of refugees (created by ISIS). And no-go zones are being created in most non-Muslim countries, even in the U.S. The number of violent events is accelerating. We in the West usually only hear about the very large events, but constant random killing of non-Muslims is happening all over the world now, as chronicled by thereligionofpeace.com. A general feeling of insecurity is increasing.
But ultimately, I believe this strategy can only fail. The people in Western nations are not as weak or as easily cowed as we may appear. They are mistaking a reluctance to fight with an unwillingness to defend ourselves — a mistake they will pay dearly for. We are nice people, for the most part, and we bend over backwards to give people the benefit of the doubt, but when we understand what is really happening, we suddenly and completely change our tune. Look what France's response has been to its latest jihad attacks: They immediately bombed the hell out of ISIS strongholds, closed their borders, arrested 104 suspected jihadis, and are shutting down the orthodox mosques in France.
People in the West are like the old man being harassed and taunted by the punks in this video. He just wanted them to go away so he could go on about his day, but when he realized they were not going to leave him alone, he knocked them out.
That's why all over Europe (and Canada and Australia) there are protests against the influx of regugees — partly out of a new understanding of the facts surrounding Muslim immigration — it produces more rapes, more criminal activity, and in the process of trying to create Muslim-only areas, non-Muslims are forced out by constant harassment. The trend is toward a growing resistance to Muslim immigration.
We can look at Flight 93 on 9/11 for a good illustration of how people in the West change their stance from relatively passive to ready to fight. The jihadis on board all the planes that day told their passengers to stay calm, and everything was going to be all right. But the people aboard Flight 93 found out about the other planes. And once they understood what was really going on, they attacked and stopped the plane from reaching its destination.
Like the people on Flight 93, our fellow non-Muslims may only need accurate information. We need to share with our fellow non-Muslims what ISIS plans on doing. It will create a resolve to defeat them.
The above explanation of Naji's strategy is summarized from an article by Amir Taheri. Read his article here: The Jihadis' Master Plan to Break Us.
Read a book by Naji: The Management of Savagery.