<P> On 9 May 1945 (Moscow time), Germany surrendered, meaning that if the Soviets were to honour the Yalta agreement, they would need to enter war with Japan by 9 August 1945 . The situation continued to deteriorate for the Japanese, and they were now the only Axis power left in the war . They were keen to remain at peace with the Soviets and extend the Neutrality Pact, and they were also keen to achieve an end to the war . Since Yalta they had repeatedly approached, or tried to approach, the Soviets in order to extend the neutrality pact, and to enlist the Soviets in negotiating peace with the allies . The Soviets did nothing to discourage these Japanese hopes, and drew the process out as long as possible (whilst continuing to prepare their invasion forces .) One of the roles of the Cabinet of Admiral Baron Suzuki, which took office in April 1945, was to try to secure any peace terms short of unconditional surrender . In late June they approached the Soviets, (the Neutrality Pact was still in place), inviting them to negotiate peace with the allies in support of Japan, providing them with specific proposals and in return they offered the Soviets very attractive territorial concessions . Stalin expressed interest, and the Japanese awaited the Soviet response . The Soviets continued to avoid providing a response . The Potsdam Conference was held from 16 July to 2 August 1945 . On 24 July the Soviet Union recalled all embassy staff and families from Japan . On 26 July the conference produced the Potsdam Declaration whereby Churchill, Truman and Chiang Kai - shek (the Soviet Union was not at war with Japan) demanded the unconditional surrender of Japan . The Japanese continued to wait for the Soviet response, and avoided responding to the declaration . </P> <P> The Japanese had been monitoring Trans - Siberian Railway traffic and Soviet activity to the east of Manchuria and in conjunction with the Soviet delaying tactics, this suggested to them that the Soviets would not be ready to invade east Manchuria before the end of August . They did not, however, have any real idea, and no confirming evidence, as to when or where any invasion would occur . </P> <P> The Japanese were caught completely by surprise when the Soviets declared war an hour before midnight on 8 August 1945, and invaded simultaneously on three fronts just after midnight on 9 August . </P> <Dl> <Dd> See Soviet invasion of Manchuria (1945) #Combatant forces for the tactical details of the combatant forces and of the invasion . </Dd> </Dl>

When did the soviet union declared war on japan