The Pacific War refers to the conflict in the Pacific region between the anti-fascist allied nations and Japan during the Second World War. On the morning of December 7, 1941, without declaring war, Japan employed a huge naval and air force in a surprise attack on Pearl Harbor, the main Pacific base of the U.S. navy and air force, inflicting disastrous losses on the U.S. Pacific Fleet. The following day the United States and Britain declared war on Japan, while Germany and Italy declared war on the United States. Japanese troops occupied many countries and regions in Southeast Asia and some islands in the Pacific Ocean. Later, under the heavy blows dealt by the armed forces of the anti-fascist nations in the Pacific region, Japan suffered one defeat after another. In August 1945 it surrendered unconditionally, and thereupon the war was ended.