A large part of Kedar's studies deals with the crusades and the Frankish Kingdom of Jerusalem, established in the wake of the First Crusade. In these studies he exhibits "an ability to change thinking through a rigorous and imaginative treatment of source-material that has often been ignored by others" and to "peel away unfounded assumptions and unwarranted traditions of historical orthodoxy." Topically, he has discussed the relationship of crusading and conversion; demography; intellectual, ecclesiastical, legal and military history; the relationships of the Frankish rulers with their indigenous subjects; medicine; pilgrimage; eremitism; taxation; topography; mutual perceptions of motivation by Franks and Muslims; and much more. His longitudinal examination of the descriptions of the Jerusalem massacre of July 1099, from eyewitness reports down to the present, "sets new standards for the historiographical analysis of individual events during the crusades." He has also shown that it is possible to establish the age of medieval mortars through radiocarbon datings of the organic components embedded in them. Turning to present-day developments, he analyzed the uses of the Crusader motif in Israeli political discourse, distinguishing between three approaches: a total denial of the possibility of comparison between the Frankish Kingdom and the Zionist enterprise; attempts to draw lessons from the Crusaders' failure; and taking recourse to the Crusaders in order to reinforce a political argument, usually critical of the Israeli establishment.