Japanese World War II strategy was driven by two factors: the desire to expand their territories on the mainland of Asia (China and Manchuria), and the need to secure the supply of raw resources they didn't have themselves, particularly oil. Since their quest after the former (conquest of Chinese provinces) endangered the latter (an oil boycott by the US and its allies), the Japanese government saw no other option than to conquer the oil sources in South-East Asia. Since these were controlled by American allies, war with the USA was seen as inevitable; thus, Japanese leaders decided it would be best to deal a severe blow to the U.S. first. This was executed in the Pearl Harbor strike, crippling the American battle fleet.