Japan's expansionist vision grew increasingly bold. Many of Japan's political elite aspired to have Japan acquire new territory for resource extraction and settlement of surplus population. These ambitions led to the outbreak of the Second Sino-Japanese War in 1937. After their victory in the Chinese capital, the Japanese military committed the infamous Nanking Massacre. The Japanese military failed to destroy the Chinese government led by Chiang Kai-shek, which retreated to remote areas. The conflict was a stalemate that lasted until 1945. Japan's war aim was to establish the Greater East Asia Co-Prosperity Sphere, a vast pan-Asian union under Japanese domination. Hirohito's role in Japan's foreign wars remains a subject of controversy, with various historians portraying him as either a powerless figurehead or an enabler and supporter of Japanese militarism. The United States grew increasingly worried about the Philippines, an American colony, within close range of Japan and started looking for ways to contain Japanese expansion.