A predominantly European nation on the periphery of Asia, historically many white citizens of Australia feared being demographically overwhelmed by the heavily populated Asian countries to the north. Following the attacks on Darwin and the associated fear of Imperial Japanese invasion in WWII, Minister of Immigration Arthur Calwell stated in 1947: "We have 25 years at most to populate this country before the yellow races are down on us." This concern about Australia's demographic vulnerability was a driving force behind the country's massive post-war program of European immigration.