During World War 2, the Soviet Union and The United States were both members of the Allies. I was thinking about the Battle of Midway today and was wondering if the Soviet Union had provided any support to the United States in the Pacific Ocean theater, in the war against the Empire of Japan?
With the Japanese invasion of Manchuria and attack on the Aleutian Islands, did the Soviets feel Japan to be a threat to Eastern Russia?
Wouldn't it have been helpful for the United States, and thus the Allies, for it to have had a staging base in Russia, on Sakhalin or across the Sea of Okhotsk from Japan, even if the Soviets didn't want to have direct involvement in that theater of the war?
The Soviets absolutely regarded Japan as a threat in the Far East. Soviet-Japanese agression precedes WW2. Conflicts over the region proceed even the Soviet Union with the Russo-Japanese War in the early 20th century over rival imperial ambitions of Manchuria and Korea between the Russian and Japanese Empires.
A big reason for the lack of Soviet involvement in the Pacific Theatre though, was that Stalin wanted to avoid fighting on two polar fronts as would ultimately happen to Germany.
The Japanese expansion in Manchuria in the 30s led to border violations on both sides culminating in a series of skirmishes between the Soviets and Japanese and their respective client states of Mongolia and Manchukuo between 1932 and 1939. The conflicts ended in Japanese defeat after the Soviet counter offensive in The Battles of Khalkhin Gon.
The Soviets and Japanese agreed to a cease fire on September 15th 1939. Stalin could now focus Soviet expansion westward now that his conflicts in the East were settled. The Soviet invasion of Poland proceeded on September 17th - just two days later.
Amidst expansion of the Axis powers in the following years, Stalin wishes to entirely concentrate on the p Western Front. Improved diplomatic relations with the Soviets also increasingly benefit Japan as their tensions with the US increase. So, in a bid to secure their borders, the powers sign the Soviet-Japanese Non-Agression Pact on April 13th 1941 in Moscow. Effectively agreeing to fight each others allies but not each other.
Basically, Stalin wanted to make sure the Axis powers were done and dusted before he dealt with Japan. This is the key reason there is no Soviet intervention until the very end of the Pacific Theatre or US military assets based in the USSR.
Stalin officially denounced the pact and invaded Manchuria on August 9th 1945 with a force of 1,577,725 troops. Stalin's preoccupation in Europe had come to an end after the Soviet victory over Nazi Germany so he could finally get involved in the Pacific Theatre. Regardless, the US was posturing to end the war without the help of the Soviets as they had already bombed Nagasaki on the August 6th. Ultimately, Stalin's decision to mobilize such an overwhelming force in Manchuria just 3 months after his victory in Europe was that he would have no say in peace proceedings if the Pacific Theatre closed with Soviets an official non combatant which would impede his capacity to extend Soviet influence in the far East following the war. Overwhelmed, Japan surrendered on August 15th - just 6 days after the Soviet invasion.