Political map of East Asia and the Western Pacific 11 December 1941 (Pearl Harbor and its Aftermath): On the morning of 8 December 1941 (still 7 December in Hawaii (Standard time)), Japan launched simultaneous attacks against American and British forces across the Pacific, bombing the US Pacific fleet at Pearl Harbor (Attack on Pearl Harbor) and invading Malaya (Japanese invasion of Malaya), Thailand (Japanese invasion of Thailand), Guam (Battle of Guam (1941)), the Philippines (Japanese invasion of the Philippines) and the Chinese concessions. Three days later, Germany supported Japan by declaring war on the United States (Axis Powers).