No, from what I understand, after reviewing the casualty rates on Saipan, Okinawa and Iwo Jima, the main reason was the predicted horrendous casualties we would suffer if we had to invade. The Russian thingy was just another nail in the Japanese coffin. As it was, the Russians demanded co-equal footing at the conference table. They took over the Kurile Islands and still own them today, so you can imagine what the story would be if they have taken more terrirtory.
A sidebar was that we found a letter that was sent out to the Jap prison commanders. To wit: when they heard that Americans had invaded the homeland, words to the effect of "do what is necessary" with all prisoners. Some commanders didn't wait for the invasion. Read about Palawan for just one instance.
There was also another political angle in that the Democrats feared a major backlash (with good reason), if we suffered anywhere near those predicted casualties when the president had the means to end the war sooner by dropping the bombs.
“They took over the Kurile Islands and still own them today, so you can imagine what the story would be if they have taken more terrirtory.”
Keeping the Russians out of a defeated Japan is a different motive from ‘necessary for the defeat of Japan.’
“There was also another political angle in that the Democrats feared a major backlash (with good reason), if we suffered anywhere near those predicted casualties when the president had the means to end the war sooner by dropping the bombs.”
More American lives were lost at Okinawa than in all the other major battles in the pacific up to then - combined. The other bad thing is the casulty ratio. There were 80k American casulties to 120k Japanese troops. That is what shocked the American command at the time that despite outright superiority in troop counts, that the Japanese defenders were able to hang with the Americans.