Historian Tsuyoshi Hasegawa has theorized that Japan was actually hedging their bets in the last days of the war, hoping that the Soviet Union would be kinder than the US. When the USSR declared war and invaded Manchuria, after the US had bombed Hiroshima, Japan finally surrendered. Garreth Cook considers the implications for nuclear deterrence:
Those days in August remain the only instance of nuclear war. The sheer horrors of the destruction, and the lingering poison of radioactivity, inform what has come to be called
nuclear deterrence: No sane nation would bring a nuclear attack on itself, and so having nuclear weapons deters your enemies from attacking. When two rival nations have nuclear weapons, as during the Cold War, the result is stalemate. Hasegawa’s scholarship disturbs this simple logic. If the atomic bomb alone could not compel the Japanese to submit, then perhaps the nuclear deterrent is not as strong as it seems.
Kevin Drum differs:
I think that Cook takes a step too far when he suggests that Hasegawa's research, if true, should fundamentally change our view of atomic weapons. "If the atomic bomb alone could not compel the Japanese to submit," he writes, "then perhaps the nuclear deterrent is not as strong as it seems." But that hardly follows. America in 1945 had an air force capable of leveling cities with conventional weaponry. We still do—though barely—but no other country in the world comes close. With an atomic bomb and a delivery vehicle, North Korea can threaten to destroy Seoul. Without it, they can't. And larger atomic states, like the US, India, Pakistan, and Russia, have the capacity to do more than just level a city or two. They can level entire countries.
(Photo: United States Strategic Bombing Survey, Physical Damage Division [Steel stairs warped by intense heat from burned book stacks of Asano Library, Hiroshima], November 15, 1945 from the International Center of Photography)
The Dish 