Aside from its religious veneer, Islam can easily be defined and understood by one wholly areligious word: tribalism — the bane of any democratic or pluralistic society.

The fact is, the entire appeal of Muhammad's call to the Arabs of his time lay in its compatibility with their tribal mores, three in particular: loyalty to one's tribe, enmity for other tribes, and raids on the latter to enrich and empower the former.

For seventh-century Arabs — and later tribal peoples, chiefly Turks and Tatars, who also found natural appeal in and converted to Islam — the tribe was what humanity is to modern people: to be part of it was to be treated humanely; to be outside it was to be treated inhumanely.  This is no exaggeration: Muslim philosopher Ibn Khaldun (d. 1406) described the Arabs of his time (let alone those from Muhammad's more primitive era eight centuries earlier) as "the most savage human beings that exist.  Compared with sedentary people they are on a level with wild, untamable animals and dumb beasts of prey.  Such people are the Arabs."

Muhammad upheld the dichotomy of tribalism, but by prioritizing fellow Muslims over blood relatives.  Thus, in his "Constitution of Medina," he asserted that "a believer shall not slay a believer for the sake of an unbeliever, nor shall he aid an unbeliever against a believer."  Moreover, all Muslims were to become "friends one to the other to the exclusion of outsiders."

Hence, the umma — an Arabic word etymologically connected to the word "mother" and which signifies the Islamic "Super-Tribe" that transcends racial, national, and linguistic barriers — was born, and its natural enemy remained everyone outside it.

The Islamic doctrine of al-wala' wa'l-bara' ("loyalty and enmity"), which Muhammad preached and the Koran commands, captures all this. The latter goes so far as to command all Muslims to "renounce" and "disown" their non-Muslim relatives — "even if they be their fathers, their sons, their brothers, or their nearest kindred" — and to feel only "enmity and hate" for them until they "believe in Allah alone" (Koran 58:22 and 60:4; see also 4:89, 4:144, 5:51, 5:54, 9:23, and 60:1).  These verses are in reference to a number of Muhammad's close companions, who renounced and eventually slaughtered their own non-Muslim relatives as a show of their loyalty to Allah and the believers.  One slew his father, another his brother.  A third — Abu Bakr, the first caliph — tried to slay his son, and Omar, the second caliph, slaughtered several relatives.  (For more, see the nearly sixty-page treatise "Loyalty and Enmity" in The Al Qaeda Reader.)

Hence, the jihad was born.  As only two tribes existed — the Islamic umma in one tent and the dehumanized tribes of the world in another — Muslims were exhorted to attack and subjugate all these "infidels" in order to make their Super-Tribe supreme.

In short, tribalistic blood ties were exchanged for religious — that is, Islamic — ties. 

This dichotomized worldview remains enshrined in Islamic law's, or sharia's, mandate that Dar al-Islam (the "Abode of Islam") must battle Dar al-Kufr (the "Abode of Infidelity") in perpetuity until the former subsumes the latter.

It also explains why tribal societies other than the Arabs also gravitated to and found Islam appealing.

For example, in the Turks' oldest epic, The Book of Dede Korkut (based on oral traditions), the newly converted Turkic tribes engage in pagan practices either frowned on or banned by Islam: they eat horse meat and drink wine and other fermented drinks; and their women are, in comparison to Muslim women, relatively free.  Only in the context of raids on the "infidel"—which comes to replace "tribal outsider"—are echoes of Islam evident in their lives.  "I shall raid the bloody infidels' land, I shall cut off heads and spill blood, I shall make the infidel vomit blood, I shall bring back slaves and slave-girls" is a typical pre-battle boast.  "They destroyed the infidels' church, they killed its priests and made a mosque in its place.  They had the call to prayer proclaimed, they had the invocation [or shahada] recited in the name of Allah Almighty.  The best of the hunting-birds, the purest of stuffs, the loveliest of girls ... they selected" is a typical account of these new Turkish converts' pious exploits.

Otherwise, Islam is absent from their lives. Although the Persian and Arab establishment was originally unimpressed by Turkish piety, they praised the new converts because they "fight in the way of Allah, waging jihad against the infidels" (which, then and now, always went a long way to exonerate otherwise un-Islamic behavior).

It was the same for those Mongols who embraced Islam.  As Ricoldo of Monte Croce (d. 1320) once observed, "the Tartars had adopted Islam because it was the easy religion, as Christianity was the hard one."  Whereas Islam complemented their preexisting tribal way of life, Christianity only challenged it.

So it is that Muhammad's most enduring contribution to world history is that, in repackaging the tribal mores of seventh-century Arabia through a theological paradigm, he also deified tribalism into a sort of hyper-tribalism, causing it to outlive its historic setting and dramatically spill into the modern era.  Whereas many world civilizations have been able to slough off or at least temper their historic tribalism, for Muslims to break with tribalism is to break with Muhammad and his laws — to break with cardinal Islamic teachings. 

Hence the notorious resistance to assimilation in the West, the creation of enclaves and clannish no-go zones, the incessant subversive activities of groups such as the Muslim Brotherhood and CAIR, and the sporadic flare-ups of terroristic activities and hate crimes.

Raymond Ibrahim, author of Sword and Scimitar: Fourteen Centuries of War between Islam and the West, is a Shillman Fellow at the David Horowitz Freedom Center, a Judith Rosen Friedman Fellow at the Middle East Forum, and a Distinguished Senior Fellow at the Gatestone Institute.