The Anti-Comintern Pact was agreed upon between Nazi Germany and the Japanese Empire. The pact would have other countries join later. The pact was created to have the two countries to oppose the Soviet Union. The pact was signed on November 25, 1936. In 1937, Fascist Italy joined the pact. Italy joined the pact because the United Kingdom and France gave Italy an ultimatum to either join a side of the war, or the Allies would come in and destroy Italy.
Nazi Germany also invaded Poland on September 1, 1939, which is the official event that started World War 2.