When the USA request or agreed with Russia's aid in the fight with Japan, as the inevitable defeat or invasion of Japanese home Islands was still in question, Russia agreed to a 3 month term before starting hostilities...Germany surrendered on May 8, 3 months later, when the folly or requirement of Russia to defeat Japan was no longer needed, a swift end to hostilities was required to prevent, or allow Russia to gain or take part in the terms of Japan...2 days before Russia's 1,500,000 troops swept into China, the first Atomic bomb was dropped, either as a show of force, or to a quick ending has been the topic of numerable debates... but the unlikely hood of Russia sitting idle, while Allied forces entered Japan, deciding it's fate, with a close proximity to Russia is nil, they would have taken it upon themselves to invade with or without the US consent, and helped to divide or obtain a piece of the Japanese pie.