In the lead up to the Second World War, Japan had engaged in several conflicts aimed at expanding its empire, most notably the Second Sino-Japanese War. Although maintaining its neutrality at the outbreak of war in Europe, in 1941 the Japanese military launched surprise attacks on Hong Kong, Singapore, Thailand, the Philippines, and Pearl Harbor, which had brought the United States into the war on the side of the Allies. In 1942, after they had captured Hong Kong from the British, the Japanese established several prisoner-of-war camps in Kowloon to house Allied prisoners of war.