Given the considerable negativity of the Church’s doctrines, policies, and imageries and wide-ranging popular animosity, the obvious question is how a burgeoning Jewish population could have developed across Europe in the period between 1000 and 1500. The answer lies in the fact that some—but by no means all—elements in European society were interested in fostering Jewish presence and that the Jews themselves were attracted to dynamically developing western Christendom. The most important of the majority elements committed to bringing Jews to western Christendom were the secular rulers of Europe, who saw in the Jews a valuable—largely economic—resource for their domains and a useful source of tax revenues. The interest of the rulers of Europe in the Jews and their power to create positive conditions for Jewish life constituted the key—from the majority side—to evolving Jewish circumstances in medieval western Christendom. Those rulers interested in the contribution that Jews might make to the rapidly developing economies of their domains had to provide their Jewish clients—above all else—with requisite security, and they by and large did so. Beyond security, the secular authorities also provided considerable assistance with Jewish economic activities, especially as the Jews moved into money lending from the twelfth century on. In the more advanced areas of Europe, especially England and France, governmental support for Jewish money lending seemed to many Christian observers almost a ruler-Jewish business partnership.
Governmental support for the Jews of medieval was contingent on the contribution that Jews might make to the local economies and to governmental coffers. Such contingent support could be and was diminished by any one of a number of factors—declining Jewish economic contribution and tax revenues, Church pressures toward limiting the Jews, and rising popular hostility. To an extent, many of the ruling class shared the intensifying hostility toward Jews, leading occasionally to governmental anti-Jewish violence, either in the form of physical assault or judicial persecution. Others made the considered calculation that the benefits derived from their Jews were outweighed by the liabilities and chose to banish Jews from their domains. While the edicts of expulsion were always couched in terms of ecclesiastical doctrine, i.e. the harm inflicted by Jews on Christian society, the decisions to expel almost always involved the same kind of considered reasoning that had originally fostered the invitations to Jewish settlement. As the rulers of more developed principalities and kingdoms of western Europe expelled their Jews, from the late thirteenth century on, the rulers of eastern Europe, anxious to match their more westerly colleagues in spurring the economic development of their domains, extended the kind of invitations and support that had originally spurred earlier Jewish settlement further westward.