Islamist enmity for infidels, regularly manifested in the jihad, is by now moderately well known. Lesser known, however, but of equal concern, is the mandate for Muslims to be loyal to fellow Muslims and Islam — a loyalty that all too often translates into disloyalty to all things non-Muslim, including the American people and their government.
This dichotomy of loyalty to Muslims and enmity for infidels — which, incidentally, corresponds well with Islamic law's division of the world into the abode of war (deserving of enmity) and the abode of Islam (deserving of loyalty) — is founded on a Muslim doctrine called wala' wa bara' (best translated as "loyalty and enmity"). I first encountered this doctrine while translating various Arabic documents for The Al Qaeda Reader. In fact, the longest and arguably most revealing document I included in that volume is titled "Loyalty and Enmity" (pgs.63-115), compiled by Aymen Zawahiri, al-Qaeda's number two.
I say "compiled" because most of the words are direct quotes from the Koran, the Muslim prophet Muhammad, and Islam's jurists (i.e., this doctrine is not an "al-Qaeda" phenomenon but rather permeates Islam's worldview). Those interested are urged to read the whole treatise. For our purposes, however, a few key scriptures must suffice: Koran 5:51 warns Muslims against "taking the Jews and Christians as friends and allies … whoever among you takes them for friends and allies, he is surely one of them," i.e., he becomes an infidel. According to authoritative Muslim exegete, al-Tabari, Koran 5:51 means that the Muslim who "allies with them [non-Muslims] and enables them against the believers, that same one is a member of their faith and community." Similar scriptures include Koran 3:28, 4:89, 4:144, 5:54, 6:40, 9:23, and 58:22; the latter simply states that true Muslims do not befriend non-Muslims — "even if they be their fathers, sons, brothers, or kin."