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Mr. History,

As Japan had a treaty of neutrality with the Soviet Union in WW2, why did the Soviet Union invade Manchuria and Karafuto in 1945?

While they were at it, why didn’t the USSR invade Hokkaido in Japan?

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Dear Lyndon,

The Soviet treaty of neutrality with Japan, like its earlier pact with Nazi Germany in August 1939, had never been thought of by either party as anything more than a mutually convenient but strictly temporary arrangement. For the Soviets, it allowed their forces to concentrate against Adolf Hitler’s 1941 invasion; at the same time, it freed Japan, after a very unsuccessful test of arms against the Soviets in Khalkin Gol, to focus its efforts on conquering China and fighting the Western powers in the Pacific. During the Potsdam Conference in May 1945, however, Josef Stalin pledged to commit his forces to the Allied cause in the Pacific three months after Germany surrendered. After secretly transporting much of its army across the vast length of Siberia, the Soviet Union broke relations with Japan, declared war and plunged into Manchuria on August 9—right on schedule. By September some Soviet forces had made some landings in the Kurile Islands, but their relative inexperience in amphibious warfare, combined with the usual spirited Japanese resistance, limited their progress before all armed forces stood down. Behind his promise to the Allies, of course, Stalin had hoped to make some inroads into the Far East and got what he wanted—among other things, payback by retaking Port Arthur and the establishment of a pro-Soviet regime in North Korea, though the spread of communism into China did not turn out quite the way he would have preferred.



Jon Guttman
Research Director
World History Group
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