2006 WHAT'S IN IT FOR YOU: WORLD - The global war

It's hard to believe " but less than five years ago there was no 'war on terror'. You could make the case that terrorism, the use of violence for political ends, is the world's third oldest profession. This century especially, it has flourished " from the Middle East to Europe. Sometimes, in its Irish, Basque and Palestinian versions, it has been driven by nationalism. Other varieties, in Italy and former West Germany, have been fuelled by left-wing ideology. But it had primarily been a law enforcement and intelligence problem. Then came 11 September 2001 " and America's new war.

The new enemy is radical Islam, driven by both ideology and nationalism, and embodied by al-Qa'ida, its fury directed against the West in general and the US in particular. Already the 'war on terror' has led America to embrace a new doctrine of preventive war. In its name, the US has invaded two countries " Afghanistan and Iraq " and some urge it to attack others. This amorphous conflict has already lasted longer than the Korean War and US involvement in the Second World War, and this may be only the beginning.

For George Bush and his promises, 2005 has not been a vintage year. But in the 'war on terror', in one respect at least, he has been as good as his word. 'Our response involves far more than instant retaliation and isolated strikes,' he told Congress nine days after the attacks. 'Americans should not expect one battle, but a lengthy campaign, unlike any other we have ever seen.'

And so it has been " and much has been accomplished. The al- Qa'ida of 11 September 2001, it may be argued, no longer exists. Its leadership has been decimated. In Afghanistan, the Taliban regime that long gave Osama bin Laden shelter has been swept away. Intermittently, Bin Laden and his deputy, Ayman al-Zawahiri, issue videos and audio tapes, sometimes taunting, sometimes menacing, but whose main practical purpose is to remind the world they are still at large.

The pair are assumed to be penned up in the tribal lands and mountain fastnesses of the Afghan-Pakistan border, their communications uncertain at best, their control over their followers a matter of increasing debate. Regularly, reports surface that Bin Laden is dead or dying, and that Zawahiri is the senior operational figure of the old guard.

In their place, a new terrorist reality is emerging, of a network of groups perhaps less sophisticated than al-Qa'ida in its prime, but no less difficult to counter. It is inspired by Bin Laden but probably no longer run by him. Even between al-Qa'ida and Abu Musab al-Zarqawi in Iraq, its best known field commander and a former Bin Laden protoge, the relationship is unclear. Some counter-terrorism experts now see Zarqawi as the most important figure in the movement.

Confirmation of a kind came last summer with a letter, purporting to be from Zawahiri to Zarqawi, that fell into US hands in Iraq. In it, the old commander complains that Zarqawi's brutal methods, the videotaped beheadings of hostages and the rest, alienate ordinary Muslims and reduce radical Islam's appeal.

In some respects, military success against the terrorists has made the job of fighting them harder. Now there are new adversaries, less well known to intelligence services, with fluid command structures and ad hoc alliances that are hard to expose. The old al- Qa'ida and its allies have the ability to strike targets almost anywhere in the world: a nightclub in Bali, commuter trains in Madrid, Underground trains and a bus in London, banks and consulates in Istanbul, foreigners' compounds in Saudi Arabia, and a wedding party at a hotel in Amman, Jordan.

Yet there is one striking omission from the list. Since 9/11, despite many scares, there has been no terrorist attack on US soil, or even solid evidence of sleeper cells, similar to those that carried out the 2001 attacks. Hundreds of suspects have been rounded up, but only one person has been charged in connection with 9/11, and even now the precise role of Zacarias Moussaoui in the plot is far from clear.

For the rest it has been one false alarm after another. In mid- 2002 the US government announced with much fanfare that it had caught Jos Padilla, an American citizen who converted to Islam, as he was plotting a radioactive 'dirty bomb' attack. It held him incommunicado in a naval prison for three-and-a-half years. That charge has been quietly dropped. Padilla will now go on trial in civil court this month as outrider in a terrorist group active in Afghanistan, not in the US.

In December, Sami al-Arian, a Palestinian-American professor from Florida, was cleared of charges that he was a leader of the Islamic Jihad terrorist group which has carried out bombings against Israel " a case under investigation since the mid-1990s. Meanwhile, the June 2003 convictions of three Detroit men accused of being part of a 'sleeper operational combat cell' have been overturned. The case had been the only successful post-9/11 prosecution of terrorists. But a federal judge ruled that some evidence against them had been fabricated, while exculpatory evidence had been withheld.