Every war has its cause and every conflict its context, none more so than the centuries-old ideological battle between Christian and Muslim theology.
The concept of holy war is almost as old as the religions themselves, with Christian crusades and Muslim invasions of North Africa, Asia and Europe.
From 630 Islamic armies were engaged in massive imperialist conquest that created one of the most successful empires in history, stretching from the borders of Hindu India in the East to Christian Spain in the West.
Until the failed attempt to capture Vienna in 1683 the Islamic armies mounted an almost continuous assault on Europe.
Not until 1913 would some parts of Europe be free from Muslim rule. The defeat of the Ottoman Empire in 1918 led to the secularisation of Turkey and the Turkish leader Kemal Ataturk's abolition of the Caliphate in 1924.
That act ended the Islamic empire, with the Christian West, in the form of Britain and France, in control of large areas of the realm of Islam-the Middle East we know today being largely shaped by Winston Churchill.
Conflict was inevitable. The tragic events of 9/11 were the result of a long process within Islam and the Islamic world, rather than the beginning of it-and now we have Isis and an attempt to revive the Caliphate.
No-one knows how it will end. The author, who has written extensively on the subject of the continuous struggle between Christianity and Islam, investigates the key events throughout history that led to the establishment of the state of Israel, the Islamic rage of the twentieth century, Al Qaeda, the conflict between Sunni and Shia, and the rise of Isis. ISIS: The Killing Caliphate explains the motives behind holy war and how the fighting in the Middle East is merely the latest manifestation of the ageless battle between theologies-war in the name of God.