Keep in mind, also by single-handedly fighting the Japs, that kept the Japs from attacking the Soviet Union, even though they were a bit gun-shy after Zhukov kicked their asses in 1939, but certainly if Hitler advanced far enough, Japan would have ultimately joined the fray against the Soviet Union.
The Japanese army was a world war I type of army and was no match for modern mobile army with lots of firepower.
The Soviets demonlished them in 1945 with ease.
Still in 1941 the Japanese would have been much better to leave the US alone and attack the British and start a border war with the Soviets to keep their army in the east.
The Soviets had a spy in Japan and they knew that Japan wasn’t going to attack them so Stalin moved the Siberian divisions west.
WW2 could have tuned in many places and this is one of the major turning points.