Toward the end of his life, Adolf Hitler reportedly lamented: "It is certainly regrettable that the Japanese did not enter the war against Soviet Russia alongside us. Had that happened, Stalin's armies would not now be besieging Breslau and the Soviets would not be standing in Budapest. We would together have exterminated Bolshevism before the winter of 1941." From the Japanese perspective, however, Germany's attitude of co-operatimg against the Soviets from 1939 to 1941 was one of ambivalence, even duplicity. After the Japanese defeat at Khalkhin Gol, the sudden unveiling of the Molotov–Ribbentrop Pact was met with shock and anger in Japan, which viewed the move as a direct violation of the Anti-Comintern Pact and a betrayal of their common interests. Consequently, in April 1941, Japan felt free to conclude the Soviet-Japanese Neutrality Pact, as tension with the West, particularly the United States, began to mount over the Japanese occupation of Vichy French Indochina the previous year. Amid a barrage of Allied economic sanctions throughout 1940 and 1941, the growing threat of war in the south and the sense of "tranquility" in the north tended to divert Japanese attention away from the long-planned campaign in Siberia. That shift was particularly welcomed by the Imperial Japanese Navy, which traditionally favored a policy of "Nanshin-ron" (southward expansion) and maintaining a deterrent against the Soviet Union, as opposed to the "Hokushin-ron" (northward expansion) that was favored by the Imperial Japanese Army.