On what date did negotiations take place to determine if the Soviet Union would join the Tripartite Pact ?
After Germany entered a Tripartite Pact with Japan and Italy , in October 1940 , Ribbentrop wrote to Stalin about " the historical mission of the Four Powers -- the Soviet Union , Italy , Japan and Germany -- to adopt a long range - policy and to direct the future development of their peoples into the right channels by delimitation of their interests in a worldwide scale . "