日ソ中立条約
The Soviet–Japanese Neutrality Pact caused the Soviets to make it policy to intern Allied aircrews who landed in Soviet territory after operations against Japan, but airmen held in the Soviet Union under such circumstances were usually allowed to "escape" after some period of time. Nevertheless, even before the defeat of Germany, the Soviet buildup in the Far East had steadily accelerated. By early 1945, it had become apparent to the Japanese that the Soviets were preparing to invade Manchuria, but they were unlikely to attack prior to Germany's defeat. In addition to their problems in the Pacific, the Japanese realised that they needed to determine when and where a Soviet invasion would occur.