Depriving the Japanese of oil was an early and effective tactic of the American Navy in the Pacific. The Japanese made a faulty assumption that they could defend supply lines from the Southern Zone to the Japan. In many ways, this was the downfall of Japanese naval forces in WWII. The Japanese also didn't realize that the US and Britain had long since cracked their codes, both military and diplomatic, and even when the Germans told the Japanese their codes had been compromised, they refused to believe it!
Quoting from Daniel Yergin's The Prize:
> Of Japan's total wartime steel merchant shipping, some 86 percent was sunk during the conflict and another 9 percent so seriously damaged as to be out of action by the time the war ended.
The Allies were sinking Japanese oil tankers faster than the Japanese could build new ones!
Japanese defeat in WWII can't be assigned to any single cause, but the vastly superior supply chain of the US Navy in the Pacific and the enormous petroleum production capabilities of America is surely up there.
Would America surrender if we were essentially defeated, blockaded, and the enemy were bombing our cities with impunity? Of course we would.
It isn't like America just snuck two nukes into Japan. It had totally defeated the Imperial Navy and was essentially bombing Japan without any resistance.
The comparison between Japan in August 45 and UK during the Blitz is just stupid.
Even if the Soviet attack was the last straw, it was only a straw. They were trying to use the Soviets to negotiate a better peace and it failed. This is like blaming your QB for missing the Hail Mary for losing the game. It was the first 59 minutes of game that caused you to lose.
People online (not real historians) like to hype this up to bandwagon the "US didn't win WWII, the USSR did" mythology. The truth is it was a huge combined effort.