The Allied powers referred the problem of Upper Silesia to the League after they had been unable to resolve the territorial dispute between Poland and Germany. In 1919 Poland voiced a claim to Upper Silesia, which had been part of Prussia. The Treaty of Versailles had recommended a plebiscite in Upper Silesia to determine whether the territory should become part of Germany or Poland. Complaints about the attitude of the German authorities led to rioting and eventually to the first two Silesian Uprisings (1919 and 1920). A plebiscite took place on 20 March 1921, with 59.6 per cent (around 500,000) of the votes cast in favour of joining Germany, but Poland claimed the conditions surrounding it had been unfair. This result led to the Third Silesian Uprising in 1921.