It is well-known that the term "Crusade" is problematic because it was not used by contemporaries, and only came into common use in English in the eighteenth century. Indeed, one notable historian entitled an article "Were There Any Crusades in the Twelfth Century?"  Although armed expeditions against enemies of Christendom continued across the twelfth century, formal definition was slow to emerge and took shape only in the reign of Innocent III (1198-1216) and by then they had taken many forms. In his scholarly discussion of "The Historiography of the Crusades," Giles Constable discerned four schools of thought amongst modern historians seeking to define this movement: the pluralists, the traditionalists, the populists and the generalists. 
The controversy has been most intense in discussions of the nature of the First Crusade because this expedition was the original and the model for all that came later. In many ways the most problematic of these contending schools is the populist, because its adherents hold that widespread enthusiasm was the essence of crusading, and, indeed, virtually defined a crusade. Those who champion this standpoint see the crusade as essentially a mass-movement of the religiously inspired, and they place less emphasis on the role of the papacy in originating it than those in other schools. They see the roots of the First Crusade in other militant mass-movements of the eleventh century that culminated in the events of 1095-99. With some exceptions, it has been European and notably French scholars who have adopted this position. To them it was self-evident that the crusade arose from the popular religiosity of western people, and while others have certainly shared this standpoint, notably Erdmann in his immensely influential work, populists have zeroed in on apocalyptic expectation as the major moving force which bestirred the masses and was the central characteristic of crusading in general, and of the First Crusade in particular.  There is some evidence, enthusiastically accepted by Rubenstein (318), that a belief in the coming of the last days was current in Western Europe in the eleventh century, although the subject is highly controversial. Cohn even argued that millennial belief was an expression of social discontent given religious form.  Certainly at the end of the eleventh century there was a renewed interest in the Tiburtine Sibyl, whose prophecies had an immensely powerful apocalyptic content and it has been surmised that this influenced Urban II. 
Rubenstein's book, then, is a reading of the First Crusade as an apocalyptic journey undertaken in the belief that the capture of Jerusalem would usher in a new stage of God's revelation, perhaps that revealed in the Apocalypse of St John the Divine. This leads Rubenstein to emphasise the role of Peter the Hermit in starting the crusade because so many of the possible apocalyptic passages are associated with him and his followers. Yet Guibert's story of poor men following a goose (47) to the east should be seen in the light of that author's aristocratic contempt for the poor. Moreover it may reflect some local superstition, of which there were plenty, given prominence in the turmoil of departures in 1096-97. And playing down Urban II as the originator of the crusade is really not a good idea. When the crusade was in crisis it was to Urban II--"who started this expedition, who, by your sermons caused us to leave our lands and all that was on those lands, commanded us to take up the cross to follow Christ"--not Peter the Hermit, that the leaders appealed in the autumn of 1098, and they reported their success to him in another letter at the end of the crusade a year later.
More generally, the trouble with Rubenstein's approach is that it is difficult to define what kind of expectation inspired these masses, if it inspired them at all. For Christians believed in an almighty and imminent deity, and therefore that all human activity was part of the divine economy, and there can be no doubt that the crusaders felt they were acting in His name in a very significant way. And certainly in such circumstances, especially at moments of crisis, there was nothing strange about participants speaking directly to the heavenly world in visions and receiving tangible assurances of divine support. That such revelations should use the rhetoric of the Bible is hardly surprising, but that does not mean that participants felt they were trembling on the edge of the end of all things. In September 1098 the crusader leaders wrote to Urban II and towards the end of their letter they referred to the two Jerusalems in what Rubenstein refers to as "an ecstatic, almost apocalyptic vision" (233). This ignores the possibility that this is a mere rhetorical flourish on a letter whose real political purpose was to temporize and avoid the agonizing choices that confronted the leaders of an expedition whose unity was shattered by the question of the fate of Antioch.
Rubenstein consistently emphasizes the irrational and violent in the actions of the crusaders and underestimates the Realpolitik that resulted in blatant land-grabs and produced deals with Muslim leaders and Muslim cities. The crusade was an ideological movement, but man does not live by ideology alone, and at various times it was ruled by political calculation and quarrels. Most importantly, it is sometimes hard to disentangle real events from the gloss put on them by later writers. There was cannibalism at Ma 'arrat, but it is reported in the most prosaic terms as a reaction to hunger by the anonymous author of the Gesta Francorum who was present, as was Raymond of Aguilers who takes much the same attitude, though he adds that this terrified the enemy. Fulcher of Chartres was not present and shuddered at the idea of eating human flesh, yet he too ascribes it to hunger. Interestingly, as Rubenstein says (241), this atrocity was not justified by reference to biblical passages. It was later writers, like Guibert of Nogent, who dwelt on this subject and exaggerated it. Now Rubenstein is right to say that the crusade was a new kind of war, which was at times appallingly savage, but circumstances as well as ideology contributed to this. Jerusalem was the culmination of the crusade and when the crusaders broke into the city there was a massacre, but any city was at mercy if it held out to the end. Moreover, the killing was not as total as is suggested here (290), where there is a heavy reliance for examples on secondary writers rather than eyewitnesses. Enough Muslims survived to form a suburb of Damascus and the garrison surrendered to the count of Toulouse whose men escorted them to friendly territory, while we know that many of the city's Jews were ransomed. The fact that the really horrible event (the cold-blooded massacre of Tancred's hostages on the Temple Mount) took place on the day after the capture of the city is not mentioned here. It is at least likely that this was motivated by dislike of Tancred's greed as by crusader fanaticism.
It seems to this reviewer that Rubenstein speaks too often in broad generalities and is over-keen to find evidence of apocalyptic enthusiasm. Yet this is an interesting, lively and in a way important book. It deals with the inner feelings and deepest beliefs of people, yet it has to be based on sources that are external and may have been written by people with their own axes to grind. This means that the evidence is exasperatingly difficult to pin down. While this reviewer is not convinced by the picture of the First Crusade as an apocalyptic movement, it is likely that apocalyptic expectation played a role in motivating people to go on the crusade and perhaps sometimes conditioned their behavior once they had departed. It most certainly affected the way in which they thought and wrote about it. Above all, this book, like Conor Kostick's on the same crusade, has a clear standpoint.  It is a refreshing and stimulating book which casts familiar events in a new light and makes one think about the subject in a new way.
1. Christopher Tyerman, "Were There Any Crusades in the Twelfth Century?" English Historical Review 110 (1995), 553-73.
2. Giles Constable, "The Historiography of the Crusades," in Angeliki E. Laiou and Roy Parviz Mottahedeh, eds., The Crusades from the Perspective of Byzantium and the Muslim World (Washington: Dumbarton Oaks, 2001), 1-22, at 10-15.
3. Carl Erdmann, Die Entstehung des Kreuzugsgedanken (Stuttgart: W. Kohlhammer, 1935), trans. M. W. Baldwin & Walter Goffart as The Origin of the Idea of Crusade (Princeton: Princeton University Press, 1977); Paul Alphandéry and Alphonse Dupront, La chrétienté et l'idée de croisade: Les premieres croisades, 2 vols. (Paris: A. Michel, 1954-59); Paul Rousset, Histoire des Croisades (Paris: Payot, 1957); Jean Flori, Pierre l'ermite et la premieère croisade (Paris: Fayard, 1999).
4. Richard Landes, Heaven on Earth: The Varieties of the Millennial Experience (Oxford: Oxford University Press, 2011); Norman R. C. Cohn, The Pursuit of the Millennium (London: Secker & Warburg, 1957).
5. Huguette Taviani-Carozzi and Claude Carozzi, La Fin des temps: Terreurs et prophéties au Moyen Age (Paris: Flammarion, 1999).
6. Conor Kostick, The Social Structure of the First Crusade (Leiden: Brill, 2008).