In 1915, during the First World War, Serbian Macedonia was invaded by Bulgaria, which captured Skopje on 22 October 1915. Serbia, allied to the Triple Entente, was helped by France, Britain, Greece, and Italy, which formed the Macedonian front. Following a great Allied offensive in 1918, the Armée française d'Orient reached Skopje 29 September and took the city by surprise. After the end of the World War, Macedonia became part of the new Kingdom of Serbs, Croats, and Slovenes, which became "Kingdom of Yugoslavia" in 1929. A mostly foreign ethnic Serb ruling class gained control, imposing a large-scale repression. The policies of de-Bulgarization and assimilation were pursued. At that time part of the young locals, repressed by the Serbs, tried to find a separate way of ethnic Macedonian development. In 1931, in a move to formally decentralize the country, Skopje was named the capital of the Vardar Banovina of the Kingdom of Yugoslavia. Until the Second World War, Skopje experienced strong economic growth, and its population increased. The city had 41,066 inhabitants in 1921, 64,807 in 1931, and 80,000 in 1941. Although located in an underdeveloped region, it attracted wealthy Serbs who opened businesses and contributed to the modernization of the city. In 1941, Skopje had 45 factories, half of the industry in the whole of Socialist Macedonia.