Were the nuclear bombs irrelevant to Japan's surrender in WWII ?

Excerpts from an interesting article at Boston.com:

For nearly seven decades, the American public has accepted one version of the events that led to Japan’s surrender...

In recent years, however, a new interpretation of events has emerged. Tsuyoshi Hasegawa - a highly respected historian at the University of California, Santa Barbara - has marshaled compelling evidence that it was the Soviet entry into the Pacific conflict, not Hiroshima and Nagasaki, that forced Japan’s surrender. His interpretation could force a new accounting of the moral meaning of the atomic attack. It also raises provocative questions about nuclear deterrence, a foundation stone of military strategy in the postwar period...

“Hasegawa has changed my mind,” says Richard Rhodes, the Pulitzer Prize-winning author of “The Making of the Atomic Bomb.” “The Japanese decision to surrender was not driven by the two bombings.”

Hasegawa and other historians have shown that Japan’s leaders were in fact quite savvy, well aware of their difficult position, and holding out for strategic reasons. Their concern was not so much whether to end the conflict, but how to end it while holding onto territory, avoiding war crimes trials, and preserving the imperial system...

As Hasegawa writes in his book “Racing the Enemy,” the Japanese leadership reacted [to the bombing of Hiroshima] with concern, but not panic... The bombing added a “sense of urgency,” Hasegawa says, but the plan remained the same... Very late the next night, however, something happened that did change the plan. The Soviet Union declared war and launched a broad surprise attack on Japanese forces in Manchuria. In that instant, Japan’s strategy was ruined.

Better to surrender to Washington than to Moscow... By the morning of Aug. 9, the Japanese Supreme War Council was meeting to discuss the terms of surrender. (During the meeting, the second atomic bomb killed tens of thousands at Nagasaki.) On Aug. 15, the Japanese surrendered unconditionally...

Those with an interest in military history will find much more at the Boston.com link.