At school, aged about sixteen I was asked to write an essay on one of the Byzantine emperors. The school library had several of Sir Steven Runciman’s books on Byzantine history. Next to them on the shelf were the three volumes of his History of the Crusades, which had recently been published. I read these out of interest and became fascinated. While I am not such an admirer of Runciman today - had I known it, his History was already considered old-fashioned when it appeared - I shall always be grateful to him for arousing my interest.

‘The crusades’ constitutes a vast subject in terms of time and space - or rather an array of subjects, since it includes quite different ones, such as the histories of the military orders and of the settlements established in the wake of crusades: among them the Latin empire of Constantinople, the kingdoms of Jerusalem, Cyprus and Thessalonica, the principalities of Antioch and Achaea, the duchies of Athens and Naxos, the counties of Edessa and Tripoli; Prussia, Livonia, Estonia and Finland; and large tracts of Portugal, Aragon and Castile in Spain. I began by researching the history of a military order in the east and then the thirteenth-century lawyer barons of the kingdom of Jerusalem. So I began by working on aspects of the Latin settlements in the Levant. It was only fifteen years into my career as an academic historian that I turned to the crusades themselves. As far as the history of the crusades proper is concerned, I think I am best known - and most criticised - for two things.

a) I have tried to empathise with the crusaders. This does NOT mean that I approve of what they did, but I recognise that they considered themselves to be engaged in something which was ethically worthwhile and I try to understand them on their own terms. Because I am Catholic this has led to the charge that I am sentimentally predisposed to give them the benefit of every doubt. My answer is that I say nothing which is not justified by the evidence and cannot help it if that evidence is too uncomfortable for twentieth- and twenty-first-century people to confront.

b) I am what is nowadays called a ‘pluralist’. The first edition of What were the Crusades? in fact, is supposed to have set the debate about definition going when it appeared in 1977. There are still those who find it very hard to accept that authentic crusading was taking place in regions other than the eastern Mediterranean, mostly, I think, because they cannot come to terms with the fact that the Muslim contribution becomes somewhat diluted: they cease to be the sole enemy. Most historians are now pluralist, recognising, of course, that pluralism is not a panacea, but believing that it is reasonable working hypothesis.

Of course crusaders must have had as many different visions and aspirations as any group of men and women. But the issue that confronts me and also many others is this. Many historians – and the public at large – have come to believe that a prime motivation of crusaders was materialistic. This seems to have originated in the nineteenth century, when French and British politicians, artists and historians viewed the crusades very positively in the light of contemporary imperialism. As imperialism came to be discredited in the 1920s and 1930s, the crusades, stripped of their ideology, began to be interpreted in social and economic terms by Liberal as well as Marxist economic historians. These had inherited from the imperialists the idea that crusading was an early example of colonialism and they assumed that such a powerful movement could only have been generated by economic forces, in spite of the fact that no economic history of it has ever been written. It is, therefore, not surprising that common to all theories of materialistic motivation is an absence of evidential proof. In fact, the evidence that has come to light points in a different direction, at least with respect to crusaders to the east, who seem to have been ideologically motivated.

Although what I am going to say is controversial, I find it hard to believe that there was any true distinction made in the middle ages between ‘just’ and ‘holy’ violence. It is essential in a subject like this to understand that ‘war’ is only one expression of the use of force; others are the sanctions at the disposal of a state and rebellion. From the fourth century to the sixteenth most Christian thinkers believed that God or Christ could authorise the use of force, either personally or through an intermediary. Although violence could only be employed within certain parameters, which came to expressed in the criteria of just cause, legitimate authority and right intention, there can be no doubt that the idea that in certain situations the use of force was not merely condoned by God but was positively pleasing to him, became embedded in Christian thought. Until the nineteenth century, moreover, the majority opinion was that acts of violence were not in themselves evil, but were morally neutral and took ethical colouring - bad or good - from the perpetrators’ intentions. But crusade theory went far further than that. Crusading was underpinned by the idea that it was ‘penitental’ and this raised it on to the same plane as prayer, fasting and works of mercy.

Most crusaders went home once their campaign was ended. Crusading was hugely expensive and very few of them returned with anything worthwhile. How would they have found the means to carry great wealth back with them even had they won it? There were gains to be made in Spain, although relatively few outsiders fought there, but in the Baltic, where in the fourteenth century crusading was run by, and for the benefit of, the Teutonic Knights, it looks again as though it was as expensive and unrewarding as it was in the east. It has been recognised for a long time that by 1300 the French nobility had overstretched itself financially on the crusades.

I am sure that most crusaders were aware of what they were doing. But at the same time the preachers, who were the main recruiters, had developed techniques of arousing crowds to the extent that when men and women were asked to step forward to commit themselves publically to take a vow which was enforceable in church law, there were probably many who found themselves spurred by the rhetoric to do something they - and their families who had to find the money - must have regretted later.

Pope Urban II, the preacher of the First Crusade in 1095-6. The idea of penitential war can be dated to the early 1080s, when Pope Gregory VII ‘ordered...Mathilda (of Tuscany) to fight the emperor Henry for the remission of her sins’. It was pointed out at the time that such a command was unprecedented – as indeed it was - and that Gregory was ‘inciting to bloodshed... secular men seeking release from their sins’. His justification for it was explained by a priest when he transmitted a blessing to Mathilda’s army in 1085. ‘We were (he wrote) to impose on the soldiers the danger of the coming battle for the remission of all their sins.’ But it would never have been easy to justify the inflicting of pain and loss of life, with the consequential distortion of the penitent’s internal dispositions, as a penance simply because he was exposing himself to danger, however unpleasant the experience might have been for him. Urban’s achievement was to give the idea a context in which it could be presented more convincingly, because he linked warfare to the most charismatic of all traditional penances, pilgrimage to Jerusalem, associating the physical liberation of the Holy Sepulchre with devotional journeys to it. This had a theoretical advantage over Gregory’s formulation, because violence was now associated with an act which was indubitably penitential. The danger and physical hardships of the coming expedition still had significance of course, but they no longer provided the main justification for treating the war as a penance; instead they gave added value to a penance which was primarily justified through its association with pilgrimage.

But after Urban there are a succession of great churchmen who were responsible for developing the theory and establishing the institutional framework. From the twelfth century to the seventeenth the consensus of the teaching of the bishops was that qualified men had a moral obligation to volunteer. This was reinforced by the support of men and women universally regarded as saints: Bernard of Clairvaux, Thomas Aquinas, Bridget of Sweden, Catherine of Siena, even probably Francis of Assisi. From Urban II in 1095 to Innocent XI in 1684 pope after pope wrote or authorised the despatch of letters, including many general ones, in which the faithful were summoned to crusade, offered spiritual privileges if they responded and threatened with divine judgement if they did not. These letters comprise an impressive, coherent and consistent body of teaching on the ethical value of crusading. The popes also recognised a new type of religious institute in approving of and privileging the military orders. And at least five general councils legislated for crusades. Two of them, the Fourth Lateran Council (1215) and the Second Council of Lyons (1274), published the constitutions Ad liberandam and Pro zelo fidei, which were among the crusading movement’s defining documents.

The French were the first to describe their contemporary imperialist ventures in crusading terms. Their occupation of Algeria in 1830 was compared to St Louis’s descent on Tunis in 1270 and in an abridged edition of Michaud’s Histoire published in 1838 his collaborator Jean-Joseph Poujoulat averred that "the conquest of Algiers in 1830 and our recent expeditions in Africa are nothing other than crusades." [Adam Knobler, "Saint Louis and French Political Culture," Medievalism in Europe II. Studies in Medievalism, ed. Leslie J. Workman and Kathleen Verduin, 8 (Cambridge, 1996), pp. 159-61.]

The idea of the crusade as an instrument of nationalism and imperialism was reinforced by the First World War and its aftermath. The war itself generated crusading rhetoric in many of the countries involved, [Elizabeth Siberry, The New Crusaders. Images of the Crusades in the Nineteenth and Early Twentieth Centuries (Aldershot, 2000), pp. 87-103] but more importantly a British army invaded Palestine and in the dismemberment of the Ottoman empire which followed - leading indirectly to the abolition of the caliphate in 1924 - Britain and France occupied Palestine and Syria and Lebanon under mandate from the League of Nations.

Today, for most "western" specialists on the subject the crusades are narrowly definable as Christian penitential war-pilgrimages authorized by the popes and fought by volunteers, who were privileged in various ways. And most do not consider them to have been specifically anti-Islamic, since they manifested themselves in many different theatres-of-war against many different enemies: Muslims, of course, but also Pagan Wends, Balts and Lithuanians, Shamanist Mongols, Orthodox Russians and Greeks, Cathar and Hussite heretics and even Catholic political opponents of the papacy. The crusading movement lasted for centuries, but it had come to an end before 1800. Nothing in the political, economic or military activities of the west in the nineteenth and twentieth centuries was remotely similar, however loose the rhetoric surrounding it.

But it is somewhat pedantic to engage in argument whether the policies of the developed world are "crusading" or not. Disputes about the terms we employ will not alter the facts that a very large number of people in the Islamic world, moderates as well as extremists, are attached to a history which satisfies their feelings of both superiority and humiliation and that they perceive themselves to be exploited by westerners, while the religious among them believe themselves to be threatened by values which they loathe. Since it is important for us to understand why they feel as they do, it is worrying that most people in the west are ignorant of the potent historical and moral force I have described. I have referred to a weakness in Islam, a lack of curiosity about the world beyond. But much the same criticism can be levelled at us.