The oppression of minorities has been a theme in the history of Europe. It has been a cause of dispute over territory, often resulting in war. With nation states demanding undivided loyalty of its citizens, there has been discrimination and racism, which has often led to persecution, at its most extreme in the Nazi crusade against the Jews. This is a history of European minority communities. It deals with the dispersed minorities, the Jews and the gypsies, as well as the muslims of the Balkans and the diaspora of Germans in eastern Europe from the Middle Ages to 1945. Almost all countries have disadvantaged ethnic and linguistic minorities; whether minorities without their own states, such as the Breton, Scots, Vlachs and Kurds; or those such as the Russians in Estonia or the Greeks in Turkey, who form linguistic groups different from the native majorities. During wars the existence of alien communities often led to persecution, in turn bringing huge refugee migrations. The result has been the resettlement of European populations. Since World War II the demand for cheap labour has led to an influx of immigrants from outside Europe. This followed a wave in which workers from the poor Mediterranean countries travelled north to industrial heartlands. Although all EEC countries now operate strict controls on immigrants, there is pressure from the east, following the fall of Communism, and from the Third World, where birth rates outstrip that of Europe. The existence of this pressure is a determinant of Europe's history in the 21st century.