At a time when Americans are reassessing so many painful aspects of our nation's past, it is an opportune moment to have an honest national conversation about our use of nuclear weapons on Japanese cities in August 1945. The fateful decision to inaugurate the nuclear age fundamentally changed the course of modern history, and it continues to threaten our survival. As the Bulletin of the Atomic Scientists' Doomsday Clock warns us, the world is now closer to nuclear annihilation than at any time since 1947.

The accepted wisdom in the United States for the last 75 years has been that dropping the bombs on Hiroshima on Aug. 6, 1945, and on Nagasaki three days later was the only way to end the World War II without an invasion that would have cost hundreds of thousands of American and perhaps millions of Japanese lives. Not only did the bombs end the war, the logic goes, they did so in the most humane way possible.

However, the overwhelming historical evidence from American and Japanese archives indicates that Japan would have surrendered that August, even if atomic bombs had not been used — and documents prove that President Truman and his closest advisors knew it.

The allied demand for unconditional surrender led the Japanese to fear that the emperor, who many considered a deity, would be tried as a war criminal and executed. A study by Gen. Douglas MacArthur's Southwest Pacific Command compared the emperor's execution to "the crucifixion of Christ to us."

"Unconditional Surrender is the only obstacle to peace," Foreign Minister Shigenori Togo wired Ambassador Naotake Sato, who was in Moscow on July 12, 1945, trying to enlist the Soviet Union to mediate acceptable surrender terms on Japan's behalf.

But the Soviet Union's entry into the war on Aug. 8 changed everything for Japan's leaders, who privately acknowledged the need to surrender promptly.