Germany was known in medieval Hebrew by the biblical name of Ashkenaz, and its Jews came to be called Ashkenazim. The expulsions and persecutions had not succeeded in ending Jewish life completely, but material and cultural conditions were poor. Excluded from the cities, the Jews tended to be dispersed in small towns and villages. There was a steady stream of emigration eastwards to Poland, where from the 13th century Jews had been attracted by grants of special privileges. This movement became even more pronounced during the upheavals of the Reformation.
The Ashkenazi immigrants in Poland were so numerous that (like the Sephardim in Turkey) they imposed their language and religious culture on the native Jews. They filled an important economic role as a middle class between the feudal aristocracy and the peasants, and they managed most of the internal and foreign trade. Neither class hatred nor religious intolerance could seriously undermine their security, and they shared in the prosperity and cultural richness of the Polish renaissance of the 16th and 17th centuries. With the cooperation of the rulers they developed a strong internal self-government which was unique in the Jewish diaspora, and the “Council of the Four Lands” (Great Poland, Little Poland, Podolia and Volhynia; there was a separate council in Lithuania) exercised wide-ranging quasi- parliamentary powers.
This golden age of Polish Jewry was brought to an abrupt and violent end during the Cossack rebellion of 1648. Among the aims of its leader, Bogdan Chmielnicki, was the eradication of Judaism in the Ukraine. Huge numbers of Jews were killed, baptized or forced to flee. According to Jewish chroniclers, over 100,000 were put to death and 300 communities were destroyed. The massacres left a deep wound on the Polish Jewish mind, and the image of the rampaging Cossacks still haunts some Ashkenazi Jews to this day: it has entered Jewish mythology in the same category as the crusades and the Spanish expulsion. The Chmielnicki massacres were only a foretaste of violence which was to beset the Polish Jews periodically, culminating in the Nazi holocaust. Their immediate result was to inaugurate a gradual movement back towards the west, at first to Germany and ultimately to those new centers that had been pioneered by the Portuguese.
Poland was not emptied of Jews—in fact its Jewish population continued to grow dramatically, so that by the early 19th century it contained over half the Jews in the world—but the Ashkenazi diaspora became a permanent and dominant feature of the map of world Jewry.
Conditions in Germany had in the meantime become more stable. Although Jews were still banned from many places, some smaller states had begun to readmit them. During the Thirty Years' War (1618—48) Jews had been allowed into several of the large cities, and the previous tendency to dispersal in the countryside began to be reversed. The trend to urbanization became very marked in the centuries that followed. The war also provided opportunities for enrichment to small traders connected with the army, and the supplying of armies became, until the late 18th century, a characteristic Jewish occupation all over Europe and even in North America. The numerous German courts with their extravagant habits also offered opportunities to financiers and dealers in luxury goods. Some of the "court Jews" (Hofjuden) in the late 17th century and the early 18th were amazingly wealthy and powerful. Such men were exceptional, but by their established position in German society they paved the way for a greater degree of social acceptance of Jews as such (perhaps reinforcing in the process certain anti-Jewish prejudices). They gathered around them larger circles of Jews who became progressively assimilated to the prevailing culture. But meanwhile the German communities were being swollen by immigration, and the sumptuous lifestyle of the court Jews contrasted starkly with the poverty and overcrowding of the Judengassen.
The Ashkenazi diaspora spread gradually westwards. By the end of the 18th century there were some 20000 Jews in Alsace (against the German trend they were scattered over a large number of small centers), perhaps only slightly fewer in England (again surprisingly dispersed, although the majority were in London) and, remarkably, rather more in the single city of Amsterdam, whose Jewish community had for a century been the largest in western Europe and was by now probably the largest of any city in the world. Very few of the Ashkenazim belonged to the upper crust of wealthy financiers, jewelers and importers; most eked out a tenuous existence as small traders or semiskilled workers. Despite a gradual process of acculturation the Ashkenazim in some places continued to speak Yiddish well into the 19th century. The common language helped in the integration of new waves of immigrants as well as facilitating contacts with other Ashkenazi communities. It also tended, together with other cultural differences, to distinguish Ashkenazim from Sephardim. Whereas in Mediterranean lands the Ashkenazi minorities were generally assimilated within the Sephardi communities, in the northern European centers, such as Amsterdam and London, where the Ashkenazim formed the large majority, there was little fusion of the two groups. Intermarriage was frowned on (particularly by the Sephardim, with their sense of superior culture and, perhaps, a deeply engrained feeling of racial purity deriving from the hard years in the Christian Iberian peninsula), and separate synagogues and communal organizations were maintained. In time some of the barriers were broken down, and the differences only rarely occasioned real animosity, but the descendants of the two groups still feel a sentimental attachment to their distinctive pasts