The Attack on Pearl Harbor was a surprise attack by Japan against the neutral United States naval base at Pearl Harbor, Hawaii on the morning of December 7, 1941. It led the United States into World War II. Japan was planning a war in Southeast Asia, against Britain and the Netherlands, as well as the U.S. in the Philippines. All these countries refused to sell petroleum and other war supplies that Japan needed for the Second Sino-Japanese War. Japan attacked so that the U.S. Pacific Fleet, which was a collection of ships that the United States could use in a war, would not enter that war.