The “Islamic State” is, in crucial ways, a fiction rather than a reality. A state has borders, a central government, and a bureaucratic structure. None of this is true of ISIS, although some have spoken of ISIS as a proto-state. What we have in fact is an armed, slash-and-burn military force, seeking control over ever expanding territory.
The fictional “Islamic State” permits the West to ignore the deeper threat posed by Islam to Western institutions. Islam is the antithesis of Europe. Tolerating the intolerant has time and again had disastrous consequences. The recent destruction of a Russian airliner and the attacks in Paris are only two examples.
For insight into Islam, undistorted by current controversies, a good place to start is Ignaz Goldziher’s Introduction to Islamic Theology and Law . The book has an interesting history. Invited in 1906 to deliver a series of lectures in the United States, Goldziher wrote them in German, but for reasons of health and his inability to secure a reliable English translation, he never made the trans-Atlantic voyage to deliver them. A German edition appeared in 1910, but a satisfactory English translation was not available until 1981 (from Princeton University Press).
The great Anglo-American scholar of Islam Bernard Lewis provided the introduction. Goldziher, Lewis says, was a Hungarian Jew by birth, and by virtue of interest and linguistic ability became a respected “orientalist,” as Middle Eastern scholars were called in the Vienna of his day. In Lewis’ judgment, as a guide to Muslim faith, law, doctrines, and devotions, Goldziher was much better placed than Christians to study Islam and to understand Muslims. To know rabbinic law and to submit to rules makes it easier to understand the Holy Law of Islam and those who obey it. The French philosopher Remi Brague, a great living scholar in his own right, similarly praises Goldziher as perhaps the greatest student Islam ever had.
The word “Islam,” Goldziher reminds his reader, means “submission.” The word expresses first and foremost dependency on an unbounded Omnipotence to which man must submit and resign his will. Submission is the dominant principle inherent in all manifestations of Islam, in its ideas, forms, ethics, and worship, and it is, of course, demanded of conquered peoples. Adherence to Islam not only means an act of actual or theoretical submission to a political system but also requires the acceptance of certain articles of faith. Therein lies a difficulty.
The Prophet was not a theologian. Islamic theology was necessarily the work of subsequent generations. Islam does not have the doctrinal uniformity of a church. Its history and inner dynamics, Goldziher shows, are characterized by the assimilation of foreign elements. He speaks of Islam’s dogmatic development under the influence of Hellenic thought, its indebtedness to Persian political ideas, and the contribution of Neo-Platonism and Hinduism to Islamic mysticism. Differences between Sunni and Shia stem from external influences.
Remi Brague, who holds the title of Professor of Arabic Medieval Philosophy at the University of Paris (and winner of the 2012 Ratzinger Prize), has produced an equally illuminating volume entitled The Legend of the Middle Ages: Philosophical Explorations of Medieval Christianity, Judaism and Islam . 
Addressing the genesis of European culture, Brague reminds his readers that Europe borrowed, first from the Greco-Roman world, then from an Arabic culture, and finally from Byzantium. Brague points out that for Christians revealed truth is the all-important bond. Muslim and Jewish revelations, which are presented as laws, do not pose the same problem as Christian revelation.
Reconciling religion and philosophy is an epistemological problem in Christianity, but in Islam and Judaism reconciling religion and revelation is a political problem. Furthermore, unlike Islam and Judaism, Christianity includes the Magisterium of the Church, with authority in the intellectual domain.
To illustrate the difference between Christianity and Islam, Brague draws upon the work of Ibn Khaldun, a fourteenth-century Muslim scholar. According to Khaldun the Muslim community has the religious duty to convert all non-Muslims to Islam either by persuasion or by force.
Other religious groups do not have a universal mission, says Khaldun, and holy war is not a religious duty for them, save for defensive purposes. The person in charge of religious affairs in other religious groups is not concerned with power politics. Royal authority outside of Islam comes to those who have it by accident, or in some other way that has little to do with religion, and they are under the religious obligation to gain power over other nations. According to Khaldun, holy war exists only within Islam and is imposed upon its leaders by sharia law.
Theological warrant aside, Brague asks how Islam’s greatest philosophers view jihad. He puts the question to three Aristotelians – al Farabi, Avicenna, and Averroes. All three permit the waging of holy war against those who refuse Islam – al Farabi and Averroes against Christians, Avicenna against the pagans of his native Persia.
Al Farabi, who lived in the lands where the enemy was the Byzantine Empire, drew up a list of seven justifications for war, including the right to conduct war in order to acquire something the state desires, but is in the possession of another; and the right to wage holy war to force people to accept what is better for them if they do not recognize it spontaneously.
Averroes, writing in the western part of the Islamic empire, approved without reservation the slaughter of dissidents, calling for the elimination of people whose continued existence might harm the state. Avicenna similarly condones conquest and readily grants leaders the right to annihilate those called to truth, but who reject it.
Western leaders fighting ISIS generally fail to acknowledge the genuine motivation of those committed to jihad. Whether from cowardice or woeful ignorance, they (at Europe’s peril) continue to speak of “the far reaches of ISIS,” without confronting the real threat.