Both the Soviets and the Japaneses could not afford a war on two fronts. when the soviets discovered that Japan had no intention of invading, it allowed them to move all their troops and send all their supplies to the war against Germany. there was, however, plenty of border skirmishes between the Russians and Japaneses. the largest started the rise of a Russian general named Georgy Zhukov. it was this man who organized the defense of Moscow, Leningrad and Stalingrad. he also defeated the Germans at Kursk, which destroyed the last powerful German panzer army in the eastern front. once Germany was defeated, the Russians invaded Manchuria, a Chinese province occupied by the Japanese.
Stalin worried Japan would attack the USSR on the east end of the country. He did not neet to be enticed to fight against Japan. He wanted to be the one who defeated them.
to attack Japan within three months of German surrender
The UUSR pledged to attack Japan within 3 months of German surrender.
Because of Pearl Harbor the United States declared war on Japan. Meanwhile Germany was at war with the USSR, and they wanted Japan to attack the USSR from the east. To get Japan to attack the USSR, Germany declared war on the United States in a good faith gesture towards Japan. Prior to this there was a war in Europe and Eastern Asia with the only connecting point being that Italy, Germany, and Japan were allies. Now the U.S. being right in the middle of these two wars became the connecting point.
to attack Japan within three months of German surrender
to attack Japan within three months of German surrender
to attack Japan within three months of German surrender
to attack Japan within three months of German surrender
Whether the USSR could have survived the German army at the gates of Moscow and a heavy attack by Japan in Siberia is open to speculation. It would seem fair to say that a two front war would have caused the USSR to be seriously damaged.
Both were subjected to unprovoked attack, The USSR by Germany and the US by Japan.
In 1940 Soviet Union signed a non-aggression treaty with Japan. USSR found this treaty to be beneficial for them as in June 1941 Germany launched its invasion against USSR, so Soviet Union could concentrate its troops in the west. USSR didn't want to "break" the treaty with Japan by allowing US to attack Japan from their land.
Japan attacked china in 1937 this is when they launched a fullscale attack.