We have understood for some time that lawlessness in one state can affect the peace of states and peoples, not just in the region, but across the globe. Our failure to finish the job and establish stability in Afghanistan, after the Soviets left, was paid for in blood and terror on the streets of New York just over a decade later.

What we have not so far fully realised is that the challenge of lawlessness does not just apply to states, but to the global space, too. Al-Qa'ida knows this. They use the global space as their space. Satellite broadcasting, the internet, international financial institutions, the networks of international travel - these are their chosen logistical structures. Al-Qa'ida no longer has physical bases in the military sense of the word. It has little or no structure, and only a tiny tangible physical presence. It has deliberately given up most of the attributes of physical form. Its most powerful weapon is its ability to remain an idea, an ethereal concept, floating in the global space, where it can morph, draw recruits, plan operations and execute them without any of the cumbersome and vulnerable paraphernalia of a conventional military structure. It materialises in the moment of the attack and vanishes again into the global space the moment after.

We cannot follow it there, because this space is as trackless and as lacking in effective governance by the rule of law as any desert in Africa or mountain fastness in Afghanistan. Malign global forces now have the power to destabilise and capture weak states and deal heavy blows to strong ones.

Paradoxically, our failure to bring justice to the global space also presents us with an equal and opposite threat - the possibility that globalisation will fail, leading to a plunge back into protectionism and regional competition.

The collapse of the Doha trade-liberalisation talks and the rise in protectionist sentiment in countries ranging from Europe to Latin America are all indicators that, for some at least, the struggle for the future is not how to liberalise global relationships for the benefit of all, but how to raise walls high enough to protect yourself.

And so, finally, we are being forced to confront the fact that, contrary to all the sunny predictions at the time, the end of the Cold War did not usher in a more stable world. It has brought us a more unstable one. Far from being "The End of History" as suggested by Francis Fukuyama, history is alive and kicking - and kicking rather hard at the moment. Far from being more tranquil, our global village is looking increasingly troubled. Among the issues that have come to haunt us, or come back to haunt us, are some very old geo-strategic cultural antagonisms, like the ancient struggle between Christendom and Islam, and some very new challenges such as globalization and resource competition. These were either completely invisible or on the very margins of debate a decade ago. Today, they are full-blooded, front and centre, and demand our attention.

We have very difficult decisions to take if we are to preserve our fragile living space, share out diminishing resources and cope with rising aspirations in the developing world. These decisions would be tough enough in stable times. But we are going to have to take them against the backdrop of fierce resource competition, a massive shift of global power away from the nations and economies of the West and rising radicalism in the world of faith.

Meanwhile, we in the West are facing a crisis of confidence in our own institutions and a lack of belief in the mores and creeds which used to act as a reliable and understood framework for the way we live our lives. Our leaders seem to lack both conviction and vision.

What we are involved in here is not a "War on Terror" - still less a "clash of civilisations". But a campaign for civilisation - a struggle for the values of tolerance and humanity that lie at the heart of all the great religions - all civilisations - against a new medievalism, whose proposals are those of darkness and ignorance. Our problem is that we have chosen the wrong battlefield, the wrong weapons and the wrong strategies to win this campaign. We have chosen to fight an idea, primarily with force. We seek to control territory; they seek to capture minds. We have presumed that predominant force gives us the right to impose our systems on others, when the only justification for the use of force is to assert justice and establish freedom, so that people can choose for themselves. We have responded to a self-declared global jihad, by asserting a self-declared global hegemony - the hegemony of Western models - as though there were no others. We have adopted methods which undermine the moral force of our ideas.

And so, in a battle of concepts, we have strengthened the concepts of our enemies and weakened our own and elected to fight on a battlefield where they are strongest and we are weakest.

Force has a part to play in this struggle - regrettably it nearly always does. But this is, at its heart, a battle of ideas and values; unless we realise that and can win on that agenda, then no amount of force can deliver victory.

Ashdown is a former leader of the Liberal Democrats, and was the High Representative for Bosnia and Herzegovina from May 2002 until January this year