Even without yet knowing the scale of the Soviet attack, Japan’s leaders knew that their troops could not effectively retaliate, and the Soviet declaration of war had ended any last hope of Japan’s securing Soviet neutrality or its assistance in attaining better surrender terms. Prime Minister Suzuki had met Emperor Hirohito earlier that morning and received approval to advocate for acceptance of the Potsdam surrender terms. Grave concern over Japan’s dire domestic situation and the Hiroshima bombing fortified the arguments of those pressing for immediate surrender.
In his book Downfall, Richard Frank effectively disproves both the ideas that it was because of the Soviet entry into the war as well as that Japan was willing to agree to "unconditional surrender" prior to Nagasaki.
