They did try invading Soviet territory, but got slapped so badly by Zhukov that they gave up. Permenantly; the Soviets were able to send all of their military forces west when their spy in Japan confirmed that the latter had no plans to attack them.

Some important Japanese politicians did anything they could to stop war with the USA (Mamoru Shigemitsu, a pacifist, and Fumimaro Konoye, who considered an attack on the USA to be a very bad idea) but the militarists had the ear of the emperor, and kool aid was drunk.