It is true that hardly a year went by without wars between Muslim and Christian princes. It is, of course, equally true that these wars, and to an even greater extent the commercial rela tions which continued in spite of them, appreciably affected the domestic history of each of the power blocs involved. Never theless, the relative self-containedness and self-sufficiency of the three major units remain the outstanding characteristics of medieval history. On the whole, the motivation of their political and cultural development lay within their own confines; their problems economic, political, religious were predominantly domestic.