However, according to some historians, the USSR originally had no intention of stopping at Manchuria. It was supposed to be the pre-game show of a full-scale invasion of Japan itself, which would've seen the Red Army folk-dance its way across the Pacific Ocean and squat-kick the island nation into submission.
It would have looked exactly like this.
The Soviets planned to begin their invasion in the northern Japanese island of Hokkaido in late August, a full two months before the Allied invasion, Operation Olympic, was scheduled to take place. However, Stalin kept his plan a secret from the other Allied forces and had absolutely no intention of telling them anything about it, preferring to wait until the forces of Operation Olympic stormed the shores of Japan to find him sitting in the emperor's palace watching cartoons. In fact, some theorize that Japan surrendered not because they were afraid of more atomic bombs from the U.S., but because they were afraid of the Soviets.
So what would have happened if Stalin had managed to plunge his forces into Japan before the war had ended? We'll never know, but based on how it went down with the other disputed territories, it's easy to guess. Stalin would've had a legitimate claim to, if nothing else, split the island in two once the war was over, maybe with a North and South Japan (possibly even a partitioned Tokyo), with a hotly contested border constantly patrolled on either side by varying groups of aggressively non-Japanese people.
We'll let you guess which side this would have been.
How would that have changed the complexion of the Cold War? Would Japan have still become the economic and technological powerhouse it is today? Would there have been a weird Japanese version of Kim Jong Il? It sets so many dominoes in motion that it hurts the brain to think about it.