From 1920 to 1921 he commanded the Soviet Western Front in the Polish–Soviet War. Soviet forces under his command successfully repelled the Polish forces from Western Ukraine, driving them back to Poland, but the Red Army was defeated outside of Warsaw, and the war ended in Soviet defeat. He later served as chief of staff of the Red Army from 1925 through 1928, as assistant in the People's Commissariat of Defense after 1934 and as commander of the Volga Military District in 1937. He achieved the rank of Marshal of the Soviet Union in 1935.