A wave of Albanians in the Ottoman army ranks also deserted during this period, refusing to fight their own kin. In September 1912, a joint Balkan force made up of Serbian, Montenegrin, Bulgarian and Greek forces drove the Ottomans out of most of their European possessions. The rise of nationalism hampered relations between Albanians and Serbs in Kosovo, due to influence from Russians, Austrians and Ottomans. After the Ottomans' defeat in the First Balkan War, the 1913 Treaty of London was signed with Western Kosovo (Metohija) ceded to the Kingdom of Montenegro and Eastern Kosovo ceded to the Kingdom of Serbia. Soon, there were concerted Serbian colonisation efforts in Kosovo during various periods between Serbia's 1912 takeover of the province and World War II. So the population of Serbs in Kosovo fell after World War II, but it had increased considerably before then.