Rupert Cornwell: The dispiriting truth is that Britain represents terrorism's perfect storm

It is of small consolation to those who lost fathers and mothers, sons and daughters in the bombings. Nor will it salve the wounds even of London, a city celebrated for its stoic determination in the face of adversity. But measured in cold numbers, the attacks this week were far from the worst in Europe in three decades of mayhem.

Think of the 85 dead in the Bologna train station massacre of August 1980, at the height of Italy's summer tourist season. Or of the 300 or so who died in Moscow in the terrible September of 1999; or of the 131 victims of the Madrid commuter train bombings in March 2004 - the attack on which Thursday's synchronised attack was plainly modelled. London in a sense was fortunate. It could have been far, far worse. But in another sense, the London bombings are the most frightening of all.

Terrorism, by and large, falls into two broad categories. One sort is driven by nationalism. The IRA, the Basque separatists and the Palestinians all have taken to violence to free themselves from what they perceive as colonial rule, be it by the British, the Spanish or the Israelis.

This sort of terrorism, fuelled by history and by grievances passed down the generations, presents huge challenges. It can be suppressed. But it can never be defeated by military means. The only lasting solutions are political, that address the grievances. But they are possible. Take Ireland. Albeit very slowly, we are surely edging towards a settlement. The wait may last a couple more decades. But I would wager that by the middle of this century, the Irish question will be history.

The Moscow bombings six years ago offer the same lesson. Precisely who carried them out is a matter of dispute. It may have been Chechen rebels. Equally likely, Russian agents were acting to provoke Moscow into a new onslaught on that wretched region. Either way, this particular slaughter of the innocents was "nationalist" terrorism. As is obvious to anyone beyond the Kremlin, by razing Grozny to the earth Russia has merely succeeded in fusing Chechen nationalism with the most murderous Islamic extremism.

And the same goes for the most intractable conflict of all, between Israelis and Palestinians. Extremists on both sides may thwart every effort to secure peace. But a genuine two-state arrangement can resolve the Israeli-Palestinian conflict.

The second strain of terrorism is the ideological-political variety that started in Germany in the late 1960s, and took its most deadly shape in the Italy of the late 1970s and early 1980s. In Greece, it experienced a lingering afterlife until the final dismantling of the 17 November group a couple of years ago.

This sort of terrorism stems ultimately from failings in a country's political system - usually the absence of any representation for the far left in the mainstream political process. A demented violence enters the mix, as left-wing groups kidnap and murder symbols of the establishment - generals, politicians, businessmen and judges - and their right-wing counterparts strike back.

Thus, almost certainly, the Bologna attack, carried out by the far right, in the hope that this atrocity, on top of others before it, would bring about the authoritarian, quasi-fascist state of which they dreamed.

For left-wing terrorists, the process was even more complicated. Their operations, the Red Brigades, Prima Linea and the rest theorised, would lead to right-wing repression, that would in turn spark the uprising of the proletarian masses that the terrorists (mostly middle-class students and intellectuals) purported to represent.

But ultimately these movements fizzled out, doomed by both the absurdity of their reasoning, and by changes in the respective national systems that drew the left fully into the political system (look no further than the former militant Joschka Fischer, now leader of the Green Party and Foreign Minister of Germany).

What is so frightening about London is that the Islamic extremists who are assumed to be have been responsible draw on both wellsprings, the nationalist and the ideological. Clearly, it is driven in part by nationalistic conviction that the West's intrusion into the Muslim heartlands of the Middle East is colonialism by another name.

Tony Blair may vow that the terrorists will never destroy "our way of life" (shades of George W. Bush's fatuous "they hate our freedom"), as if al-Qa'ida and its spin-off organisations were an existential threat to the nation, comparable to Hitler's Germany. The reality is they want Britain out of Afghanistan and out of Iraq. They got Spain out with the Madrid bombings, so why not try the same tactic in London?

But this nationalism is driven by ideology, in this case a warped interpretation of the religion of Islam, and the belief that the "war on terror" is a war on Islam. This may not be quite "the clash of civilisations" (geopolitical Islam is too fractured and poly-centric for that). But Islamic culture tends to resist the influence of the West, rather than be assimilated by it. And that goes even when pockets of Islamic culture are physically implanted in the West - in this case Europe.

Consider 11 September 2001. The attacks on New York and Washington were conceived abroad, financed from abroad, and carried out by people from abroad (15 of the 19 hijackers were Saudis with passports issued in Saudi Arabia). There is no evidence they were supported, ideologically or otherwise, by Arab-Americans.

Deride and sneer at Bush's America if you will, but the enduring ability of the US to assimilate people from other lands and other cultures is extraordinary. Not so Britain, France and other European countries, with their substantial and largely un-integrated Islamic minorities. The proportion who hold extreme views may be tiny. But it needs only half a dozen fanatics to carry out four bombings like those in London.

British links with Islamist terrorism are uncomfortably numerous; look no further than Richard Reid, the "shoe bomber" who came within an ace of blowing up a transatlantic flight in December 2001, and Ahmed Omar Sheik, the mastermind of the kidnap and murder of the journalist Daniel Pearl in Pakistan in 2002 - both of them subjects of Her Britannic Majesty.

Borders in Britain and Europe may be far more porous than those of the US, but I would hazard no bet that that the London bombings were exclusively the work of short-term visitors to our islands. The dispiriting truth is that Britain represents terrorism's perfect storm. Among a few who live there, the ideology already thrives. Its partnership in the invasion of Iraq makes it a natural target for "nationalist" Islamic radicalism. Finally, the Channel, with a tunnel running underneath it, cannot match the Atlantic and Pacific as a natural barrier. The wonder is not that London was bombed, but that it took so long to happen.