On 7 December 1941, Japanese naval and air forces attacked the American Pacific Fleet base at Pearl Harbor on the Hawaiian island of Oahu.  No declaration of war was made.  The attack was one of the most important events of the twentieth century.  It brought the United States of America into the Second World War and, together with the German assault on the Soviet Union in June 1941 and Hitler's declaration of war on America on 11 December, turned a series of regional campaigns into a true world conflict.  Although two mighty alliances now faced each other, the addition of America's vast industrial power to their cause virtually assured the eventual victory of the USA, Britain and the Soviet Union.