This post was updated on May 27, 2016, to incorporate Barack Obama’s remarks at Hiroshima.

As advertised, President Obama did not apologize for the U.S. nuclear strike that destroyed the city of Hiroshima on August 6, 1945, on his recent visit to the city. Instead, he issued a vacuous call for the courage to “spread peace and pursue a world without nuclear weapons.” Steering clear of any specific reference as to why the United States chose to incinerate over 100,000 Japanese, he orated that “We come to ponder the terrible forces unleashed in the not so distant past. We come to mourn the dead … their souls speak to us and ask us to look inward. To take stock of who we are and what we might become”—a rhetorical exercise that in essence amounted to little more than Donald Rumsfeld’s infamous “stuff happens.” Seventy years after World War II, it seems the nuclear attacks on Hiroshima and Nagasaki are still a matter for evasion, justified by U.S. officials as the only way to end the war and save American lives. To fill in Obama’s omissions, I turned to the historian Gar Alperovitz. His 1995 book The Decision to Use the Atomic Bomb and the Architecture of An American Myth is the most definitive account we are likely to see of why Hiroshima was destroyed, and how an official history justifying that decision was subsequently crafted and promulgated by the national security establishment. As he explained, the bomb not only failed to save Americans lives, it might actually have caused the needless deaths of thousands of U.S. servicemen.

Let’s start with the basic question: was it necessary to drop the bomb on Hiroshima in order to compel Japanese surrender and thereby save American lives?

Absolutely not. At least, every bit of evidence we have strongly indicates not only that it was unnecessary, but that it was known at the time to be unnecessary. That was the opinion of top intelligence officials and top military leaders. There was intelligence, beginning in April of 1945 and reaffirmed month after month right up to the Hiroshima bombing, that the war would end when the Russians entered [and that] the Japanese would surrender so long as the emperor was retained, at least in an honorary role. The U.S. military had already decided [it wanted] to keep the emperor because they wanted to use him after the war to control Japan.

Virtually all the major military figures are now on record publicly, most of them almost immediately after the war, which is kind of amazing when you think about it, saying the bombing was totally unnecessary. Eisenhower said it on a number of occasions. The chairman of the Joint Chiefs said it—that was Admiral Leahy, who was also chief of staff to the president. Curtis LeMay, who was in charge of the conventional bombing of Japan, [also said it]. They’re all public statements. It’s remarkable that the top military leaders would go public, challenging the president’s decision within weeks after the war, some within months. Really, when you even think about it, can you imagine it today? It’s almost impossible to think of it.

Had the United States ever wanted the Russians to come in?

Here’s what I think happened. Not knowing whether the bomb would work or not, the top U.S. leaders were advised early on that the Russian declaration of war, combined with assurances that the emperor could stay on in some titular role without power, would end the war. That’s why at Yalta [the February 1945 summit between Roosevelt, Stalin, and Churchill] we desperately begged the Russians to come in, and they agreed to come in three months after the German war ended.

U.S. intelligence early on had said this would end the war, which is why we sought their involvement before the bomb was tested. After the bomb was tested, the United States was desperately trying to get the war over before they came in.

Is it possible that the U.S. leadership avoided actions that might have brought about surrender, to keep the whole thing going so that they would have an excuse to use the bomb?

Now you’ve put your finger on the most delicate of all questions. We cannot prove that. But we do know that the advice to the president by virtually the entire top echelon of both military and political leaders was to give assurances to the Japanese—that would likely bring about a surrender earlier in the summer of 1945, after the April intelligence reports.

Had they given those terms at that time, as many of the top leaders suggested—Under Secretary of State [Joseph] Grew for instance, and Secretary of War [Henry] Stimson as well—the war might very well have ended earlier, even before the Russians came in.

The allied leaders meeting at Potsdam in late July issued the Potsdam Declaration laying the surrender terms for the Japanese. In your book, you discuss an attempt to include the necessary assurances about preserving the emperor in the declaration. What happened?

As originally written, paragraph twelve of the Potsdam Declaration essentially assured the Japanese that the emperor would not be taken off of his throne, and [would] be kept on in some titular role like the king or queen of England but with no power. It was a recommendation of everyone in the top government, with the exception of Jimmy Byrnes. Byrnes was the chief advisor to the president on this matter, and he was secretary of state. There’s no doubt that he controlled the basic decision-making on it. He was also the president’s personal representative on the interim committee, which considered how, not whether, to use the bomb. He was the man who was directly, in this case, in charge. They all thought the war would end once that was stated, and they knew the war would continue if you took out paragraph twelve, and Jimmy Byrnes took it out, with the president’s approval.

So that was a deliberate effort to prolong the war?

I think that’s true, but you can’t prove that. The U.S. Joint Chiefs of Staff, facing a blockage by Byrnes, found a way to get the British Chiefs of Staff to go to Churchill to go around Byrnes to Truman to try to get him to put the paragraph back in, which Churchill in fact did. Truman did not yield. He followed Byrnes’ advice. A remarkable moment.

What was the justification for Nagasaki?

Well, the claim was that it was an automatic decision. The decision had been made to use them when they’re ready. I think the scientists, and then also the military, Groves in particular, wanted to test the second one.

There is another reason I think was probably involved. The Red Army had entered Manchuria on August 8, and Nagasaki was bombed on August 9.The entire focus of top decision-making, which means Jimmy Byrnes advising the president, at this point in time . . . we’re now past whether or not to use the bomb . . . was whether you could end the war as fast as possible, as the Red Army was advancing in Manchuria. The linkage logically between that and “Is that why Nagasaki went forward?” or, rather, “why it was not aborted” is impossible to make with the existing documents, but there’s no doubt that the feeling and the mood in the top decision-makers was on “How do we end this damn thing as fast as we can?” That’s from a context in which the decision to hit Nagasaki either was made, or rather, not questioned.

The official line, that we had to do it, the bomb saved lives, the Japanese would have fought to the last man, and so forth, set in hard and fast fairly quickly. How do you account for that?

Harper’s Magazine played a major role. They published what was basically a dishonest piece by the former secretary of war, Henry Stimson. There was in fact mounting criticism after the war, started by the conservatives, not by the liberals, who defended Truman, which was then opened up by the military, and then some of the scientists, and then some of the religious leaders, and then the article in the New Yorker, John Hersey’s “Hiroshima.”

There was sufficient criticism building in 1946 that the leadership thought it had to be stopped, and so they rolled former Secretary of War Stimson out to do a strong defense of it. It was actually written by McGeorge Bundy [later National Security Adviser in the Vietnam years], and they got Harper’s Magazine to publish it [in February of 1947]. The article became a major report all over the country, and it became the basis of reporting in the newspapers and radio at that time. I think it’s correct to say that it shut down criticism for roughly two decades.

Well, we can consider this interview an act of expiation. Was it important for U.S. foreign policy going forward to convince the country and the world we had not done a bad thing but a good thing by ending the war and saving lives?

Yes, on two levels. Hiroshima and Nagasaki were not military targets. That’s why they had not been attacked, because they were so low in the priority list. So who was there? There were a few small military installations. The young men were at war, but who was left behind? Minimally, about 300,000 people—predominantly children, women, and old people—who were unnecessarily destroyed.

It’s an extraordinary moral challenge to the whole position of the United States and to the decision-makers who made those decisions. If you don’t justify that decision somehow, you really are open to extreme criticism, and justly and rightly so.

Enjoy this Conversation? Subscribe to Harper’s Magazine and receive our print edition delivered to your door each month—plus instant digital access to our entire 166-year archive.

If Obama is not going to apologize for the bomb at Hiroshima, what should he say?

It would be good if the president were to move beyond words to action while in the city. A good start would be to announce a decision to halt the $1 trillion buildup of next-generation nuclear weapons and delivery systems. And he might call upon Russia and other nuclear nations to join in the good-faith negotiations required by the Nuclear Non-Proliferation Treaty to radically reduce nuclear arsenals.