Japan, which had recently signed the Anti-Comintern Pact with Nazi Germany, was blindsided by the Non-Agression Pact.
After the Soviets defeated the Japs at the Battle of Khalkhin Gol in 1939, the Japs went on to basically sign their own Non-Aggression Pact with the Soviets, something Hitler might like to have known, when he declared war on the US.
“something Hitler might like to have known, when he declared war on the US.”
Hitler knew. Japan was already in the Axis when they signed with the Soviet Union. Hitler blindsided Japan again with Barbarossa. He made no arrangements with Japan to attack the SU, and the terms of the Axis pact didn’t require Japan to join in, so they didn’t.