In order to further their own faction, relatively junior officers resorted to the assassinations of members of the rival faction and their supporters in government. With both factions being opposed to the peace faction, this period has become known as the era of government by assassination. Insubordination by the Kwantung Army led first to the occupation of Manchuria, and later the Second Sino-Japanese War following the Marco Polo Bridge Incident. However, at the Battles of Khalkhin Gol, any farther expansion northwards into Siberia was shown to be impossible given the Soviet superiority in numbers and armour.