If I'm not mistaken, the Japanese did not surrender after the first atomic bomb. They surrendered 3 days later, after the second bomb. The second bomb moved the Japanese Emperor to surrender publicly via a radio broadcast, while a group of junior officers was fighting the Japanese military who was trying to stop their Emperor from surrendering.
And here Russia (I try to avoid terms like "Soviets" since that's just a front, in reality is was Russia moving all the strings) saw an opportunity to attack a weakened Japan, and launched an invasion against it. They took the Kuril Islands, which they hold to this day. The Kuril Islands are the reason WWII is not over yet, since Russia and Japan haven't signed.
Many people like to talk about WWIII, but actually what we're seeing in Europe right now is simply the continuation of WWII: it literally never ended, and one of the protagonists is the same one who, together with Germany as its de facto ally, launched WWII with the express purpose of conquering the world (it was believed that Communism was scientifically proven to be inevitable, and Russia simply happened to be at the helm of that inevitability; it wasn't like Russia wanted to conquer the world, it was imply that it had no choice but to do so by following the natural laws as described by the "science" of Communism).
Or at least that's as far as my knowledge of history got me!
RE: Words Matter