[AnimalMuppet]

The USSR had to carefully keep enough land forces in the Pacific region to deter a Japanese land invasion. (Remember that Japan controlled Manchukuo.) So, yes, the USSR had little involvement, and they had to be very careful to keep it from becoming an active front.

See https://en.wikipedia.org/wiki/Battles_of_Khalkhin_Gol (that was in 1939).

[dwd]

Fear of the USSR entering the war against them was also a deciding factor in Japan's surrender. More so than the atomic bombs.