God's War: A New History of the Crusades

In the eleventh century of the Christian Era, the region between the Atlantic, the Sahara Desert, the Persian Gulf, the rivers of western Russia and the Arctic Circle lived in the shadow of two great empires, Rome and the Baghdad caliphate, and accommodated two world religions, Christianity and Islam. The legacy of the classical Roman empire still determined cultural assumptions even outside the attenuated rump of the eastern Roman empire that survived as a comparatively modest but still powerful Greek-speaking empire situated between the Danube and the Taurus mountains, based on Constantinople, known to modern historians as Byzantium. In western Europe north of the Pyrenees, where Roman imperial rule had vanished five centuries before, the image of Rome, in law, art, architecture, learning and the Latin language, persisted, even in places between the Rhine and Elbe where the legions had never established their grip. The rulers of Germany claimed to be the heirs of the western Roman emperors, direct successors to the Caesars. To the east of Byzantium, the Near East, Egypt, the southern Mediterranean coastlands and most of the Iberian peninsula preserved the inheritance of the great Arab conquests of the seventh and eighth centuries, which had established an empire centred on the caliph (Commander of the Faithful, political heir of the Prophet) of Baghdad from the mid-eighth century.

Cultural divisions were reinforced and defined by religion; Christianity in Byzantium and western Europe from northern Iberia to the Elbe, Ireland to the Hungarian plain; Islam to the east and south, in western Asia, north Africa and the southern Mediterranean. Neither religious block was united. In the later tenth century, the traditional authority of the caliph of Baghdad had been usurped in Egypt by a caliph adhering to the minority Shi’ite Islamic tradition that had separated from the majority, orthodox Sunni tradition in the late seventh century over the spiritual legitimacy of the successors of the Prophet. In Spain, the Muslim community owed allegiance to an indigenous caliphate, based at Cordoba, until its disintegration and fragmentation in the early eleventh century. In Christian territories, although a sharper separation of powers existed between religious and secular authority than in Islamic states, two main distinctive forms of Christianity had developed since the later Roman empire; the Greek Orthodox tradition based on the Byzantine empire and a Latin tradition theoretically centred on the papacy in Rome but largely driven by the twin forces of local, aristocracy-led churches and a network of monasteries. In both Christianity and Islam, apparently monolithic belief systems concealed within them infinite local variety and tensions born of social, linguistic, ethnic, cultural and geographic diversity and distance. There were few non-Christians in lands ruled by Christians, although Jewish communities were spreading from the tenth century north of the Alps, especially to France and the Rhineland. By contrast, every Muslim region contained non-Muslim inhabitants, often in large numbers, mainly those Islamic law called the People of the Book, Jews and Christians, the latter from a range of local sects and confessional traditions deriving from late Roman theological interpretations different from either Latin or Greek orthodoxies.