 In 1917, Sleževičius, together with Felicija Bortkevičienė and other allies, broke away from the LDP to form the Lithuanian Popular Socialist Democratic Party.In 1917, Sleževičius, together with Kazys Grinius, joined the presidium of the newly established Supreme Council of Lithuania in Russia, based in Voronezh.Buoyed by the Act of Independence of Lithuania, the Council encouraged ideas of Lithuanian sovereignty, issued passports and assisted Lithuanians in returning to their homeland.