The Soviet Union entered World War II when Germany invaded in June 1941, and in December 1941 Japan entered the war by attacking Allied forces and territories in the Western Pacific and Southeast Asia. Although these events placed the countries on opposite sides in the war, neither had an interest in engaging in military operations against the other, both being fully occupied with the wars in which they already were involved. Thus, the countries maintained a scrupulous neutrality toward one another until almost the very end of World War II; other than inspecting cargos to ensure they did not include war materials and protesting the reflagging of American ships as Soviet ones, Japan did not deliberately interfere militarily with Lend-Lease convoys carrying war materiel from the United States to the Soviet Union in the North Pacific, and the Soviet Union turned down American requests to base American aircraft on Soviet territory for operations against Japan and ignored Allied requests for any other actions which might provoke Japan. The Soviet Union's leader, Josef Stalin, took the position that Soviet entry into the war against Japan would not be possible until after the defeat of Germany.