In 1919, Polish nationalist forces led by Josef Pilsudski succeeded in re-establishing an independent Polish state. Poland had disappeared from the map of Europe in 1794 following the third partition. It had been devoured by its traditional enemies; Prussia, Austria and Russia. Historically, Poland had been a state without fixed borders, and via a combination of changing dynastic alliances and a pattern of eastward migration, from the twelfth century formerly Slav areas east of the rivers Oder and Neisse became progressively germanicized. By 1921, following the end of World War I, several peace conferences, and after a series of referenda in disputed (former) German areas and a series of wars with all of its neighbors, including an especially successfully prosecuted war against the embryonic Soviet Union, the new state had managed to become a state which incorporated virtually all ethnic Poles. However, in addition to incorporating the overwhelming majority of ethnic Poles, the borders of the new Polish state also included huge numbers of other ethnic, religious and national groups.