Causes of the WW2 in the pacific, Litzy R. By _.litzy.rodrdriguez._ 1931 Japan invades Manchuria 1937 Japan invades China 1941 Japan invades Indochina Dec 7, 1941 Japan attacks Pearl Harbor Dec 8, 1941 The U.S. declares war on Japan Dec 11, 1941 Germany & Italy declare war on the U.S.