 By the mid-16th century, 80% of the world's Jews lived and flourished in Poland and in Lithuania; most of western and central Europe was by that time closed to Jews.In Poland–Lithuania the Jews were increasingly finding employment as managers and intermediaries, facilitating the functioning of and collecting revenue in huge magnate-owned land estates, especially in the eastern borderlands, developing into an indispensable mercantile and administrative class.Despite the partial resettlement of Jews in Western Europe following the Thirty Years' War (1618–1648), a great majority of world Jewry had lived in Eastern Europe (in the Commonwealth and in the regions further east and south, where many migrated), until the 1940s.