南滿洲鐵道
Japanese economic presence and political interest in Manchuria had been growing ever since the end of the Russo-Japanese War (1904–1905). The Treaty of Portsmouth that ended the war had granted Japan the lease of the South Manchuria Railway branch (from Changchun to Lüshun) of the China Far East Railway. The Japanese government, however, claimed that this control included all the rights and privileges that China granted to Russia in the 1896 Li–Lobanov Treaty, as enlarged by the Kwantung Lease Agreement of 1898. This included absolute and exclusive administration within the South Manchuria Railway Zone. Japanese railway guards were stationed within the zone to provide security for the trains and tracks; however, these were regular Japanese soldiers, and they frequently carried out maneuvers outside the railway areas.