By 1940, Japan had conquered much of the Chinese coast and major river valleys but had been unable to defeat either the Nationalist government of Chiang Kai-shek or the Communist forces under Mao Zedong. Though Japan's government was nominally led by the civilian government of Prime Minister Fumimaro Konoye, Minister of War Hideki Tojo and other military leaders held immense power in the Japanese governmental system. At Tojo's insistence, Japan moved to take control of lightly-defended European colonies in Southeast Asia, which provided important resources as well as a conduit of supply to Chinese forces. When Japan occupied northern French Indochina in late 1940, Roosevelt authorized increased aid to the Republic of China, a policy that won widespread popular support. He also implemented a partial embargo on Japan, preventing the export of iron and steel. Over the next year, the Roosevelt administration debated imposing an embargo on oil, the key American export to Japan. Though some in the administration wanted to do everything possible to prevent Japanese expansion, Secretary of State Hull feared that cutting off trade would encourage the Japanese to meet its needs for natural resources through the conquest of the Dutch East Indies, British Malaya, British Burma, or the Philippines.