On September 1st, 1939, World War 2 began. Initially, Japan was not involved. Japan was already at war with Asia in 1937, but got involved after they bombed Pearl Harbor in 1941. Even though a vast majority of the conflict was between Japan and America, most combat happened in Europe and East Asia.
In 1941, America decided to place an embargo on Japan. This meant that the Japanese couldn’t export steel, scrap iron, and aviation fuel to their country. Japan obviously got angry over this.