The year 2001 was meant to be the United Nations Year of Dialogue between Civilizations. Instead, the phrase most widely quoted was Samuel Huntington's prediction of a "clash of civilizations".
The most prophetic work of our time has turned out to be Benjamin Barber's 1992 essay, Jihad v McWorld. In it, he spoke of the imminent collision of two opposed forces, tribalism and globalism, "both bleak, neither democratic", the latter driven by international markets, the former by resurgent local hatreds. That is what happened on September 11, and neither underlying cause is about to disappear.
September 11 was the most shocking experience I have lived through. It wasn't just what happened; it is what we began to realize could happen. We knew that however bad the New York and Washington tragedies were, worse could happen.
Before September 11, much attention was given to globalization. Far too little was paid, despite the warning signals, to the return of religion in its most virulent form. Civilizations. are at risk when they are blind, and for centuries Europe has been blind to the possibility that religion was neither dying nor dead but mutating into new and sometimes deadly forms.
Our world now faces challenges on many fronts. We do not yet know how to guard against terror while preserving freedom and mobility. There are unknowns in all directions, and the battle has hardly begun. One thing, though, is clear. The nation-state is becoming an ever less salient factor in global politics. It has become too big for the small problems and too small for the big ones. Increasingly, the gap it leaves is being filled by the world faiths. Religion has become a major force in shaping world events - and if it does not become part of the solution, it will certainly be part of the problem.
The creative and destructive powers of the great faiths often go together. Religions bind people together as communities; that is their strength in an age when other structures of meaning and relationship are in disarray. But the very walls we build around ourselves for mutual protection, divide us from those who stand outside; every "us" creates a "them". That is why religions, though they promote peace within their borders, can inspire war across them.
Humanity has been here before. The pages of history are stained with the blood shed in crusades, jihads, inquisitions, pogroms, and the wars of religion that scarred the face of Europe in the 16th and 17th centuries. In the past, most people were surrounded by others with whom they shared a history, traditions and a creed. Today, our lives are enmeshed with conflicts far away and cultures utterly unlike our own. Never before have religions been confronted more fatefully with the challenge of making space for difference - the other, the infidel, the unredeemed.
Can we see God's image in one who is not in our image? Can we hear His voice in accents unlike our own? Can we learn to love the stranger? God has given us many faiths, but only one world in which to live together, and it is getting smaller all the time.
It took the death of George Harrison to remind us of the long lost days of the Beatles, when all you needed was love and all we were saying was give peace a chance. The world has grown darker since but, from time to time, the clouds part and, when they do, I still hear echoes of George singing, "Here comes the sun". We've lost him, but the song remains, and with it a fragment of a not-yet- extinguished hope.
Rabbi Professor Jonathan Sacks is chief rabbi of the United Hebrew Congregations of the Commonwealth.
© Guardian Newspapers Limited 2002