On 15 August 1919, German border guards  massacred ten Silesian civilians in a labour dispute at the Mysłowice mine . The massacre sparked protests from the Silesian Polish miners, including a general strike of about 140,000 workers, and caused the First Silesian Uprising against German control of Upper Silesia. The miners demanded the local government and police become ethnically mixed to include both Germans and Poles. About 21,000 Germans soldiers of the Weimar Republic's Provisional National Army , with about 40,000 troops held in reserve, quickly put down the uprising. The army's reaction was harsh; and about 2,500 Poles were either hanged or executed by firing squad for their parts in the violence. Some 9,000 ethnic Poles sought refuge in the Second Polish Republic, taking along their family members. This came to an end when Allied forces were brought in to restore order, and the refugees were allowed to return later that year.. What year were Polish refugees allowed to return after the First Silesian Uprising?