Both Europe's Christian majority and its Jewish minority have often envisaged Western Christendom as the site of an age-old and continuous Jewish settlement. In fact, however, down through the end of the first Christian millennium, Jews formed only a tiny portion of the population of Latin Christendom, and they constituted only a miniscule fraction of world Jewry. For the first half of the Middle Ages (roughly the sixth through tenth centuries), the overwhelming majority of Jews lived under Muslim domination, with a substantial number making their residence in Eastern Christendom under Byzantine rule. Western Christendom was a distant third in terms of the Jewish population it hosted and the power and creativity of that population. Even in Europe, the largest Jewish communities were to be found in areas under Muslim control, such as most of the Iberian Peninsula and southern sectors of Italy.

This distribution of world Jewry reflects the relative power of the three major power blocs during the first half of the Middle Ages: the dominant Islamic bloc, the still-potent Greek Christian bloc, and weak and backward Latin Christendom. Significant change in world Jewish demography was the result largely of alterations in the patterns of economic, political, and military power in the Western world, as Christian Europe, beginning around the year 1000, unexpectedly surged forward in population, economy, military might, political organization, and cultural creativity. As Western Christendom advanced, it became home to an increasingly large Jewish population.