Every summer, as the anniversaries of the U.S. nuclear strikes on Hiroshima and Nagasaki approach, Americans engage in the painful moral exercise of wondering whether President Harry Truman should have ordered the use of nuclear weapons (or as they were called at the time, the “special bombs”) against Japan in August 1945. And every year, as we get farther away in time from those horrible events, we wonder if we were wrong.

In 1945, Americans overwhelmingly supported the use of the bomb; seventy years later, that number is now a bare majority (some polls suggest less), with support for Truman’s decision concentrated among older people.

Truman, for his part, thought he was bringing the war to a swift close. Taken in its time, the decision was the right one. As historian David McCullough has been known to say, “people living ‘back then’ didn’t know they were living ‘back then’,” and to judge the decisions of people in 1945 by the standards of 2015 is not only ahistorical, it is pointless. Truman and his advisers made the only decision they could have made; indeed, considered in the context of World War II, it wasn’t really much of a decision at all.

There are three arguments usually marshalled against the use of the bomb in 1945. First, that to use the bomb only against Japan was racist; second, that it was pointless; and third, that it was done purely for political effect that had more to do with the Soviet Union than with the war in the Pacific. These objections make little sense when weighed against counterfactual thinking about American alternatives.

Was the use of nuclear bombs against Japan actually racism? Would Truman have used the bomb against the Germans? After all, America had a “Germany first” strategy from the very beginning of its involvement in the war, so why drop the bomb on Japan? Was American nuclear devastation reserved only for Asians but not Europeans?

It is difficult to believe that the Allies would have spared the Germans anything after turning the streets of German cities like Dresden to glass under repeated firebombing. The more obvious objection, however, is that the first atomic test took place in July 1945, two months after the Nazi surrender in May. There is some evidence that FDR’s advisers thought about using the bomb against Germany, but by the time Truman took office, it was a moot point: the Nazis were beaten and the invasion of Germany was winding down, not gearing up.

Truman’s detractors, in the absence of any evidence, merely claim that Truman would have done no such thing, especially at a time when so many Americans were of German descent. There is no arguing with this point, as I learned in the mid-1990s. At the time, I was teaching at Dartmouth College, where I had a chance encounter with a well-known historian on the subject. Truman’s papers had been unsealed in those years, and there was no evidence that Japan was singled out for any other reason than it was still fighting. (Indeed, the Americans specifically tried to seek out military targets rather than simply to butcher the Japanese.)  

I asked this colleague what he thought of the new evidence. “I don’t care,” he said. For people who hold to the “it was about racism” theory, that’s about as far as you’re going to get.

But what about a stronger objection, that Truman should have realized that Japan was beaten? This is one of those arguments that assumes modern-day omniscience on the part of historical figures. The fact of the matter is that Japan was not preparing to surrender; it was preparing to fight to the death. The invasion of the Japanese home islands was not going to look like the invasion of Germany, where the Nazi armies were crushed between advancing U.S. and British forces on one side and an avalanche of enraged Soviet troops on the other. The Japanese invasion, on the other hand was likely to cost a half-million Allied and Japanese lives— all in what should have been the last months of the war.

Here, I will candidly admit that I am not objective about this question. In 1945, my father finished infantry school in Georgia and was immediately shipped to California to await his orders to carry a rifle during the invasion of Japan. Fortunately, as things turned out, he did nothing more than fight “the Battle of Fort Ord,” as my mother wryly called it. My father, for the remainder of his life, considered nuclear weapons to be an awful and inhumane instrument of war, but he was certain that they saved his own life.

Still, let’s assume, as some historians have done, that Harry Truman was either duped or made an honest mistake, and that the invasion casualty estimates were way off. (One historian has suggested that these estimates were ten times too high.) What should Truman have done? If the figure of 500,000 casualties was wrong, perhaps Truman would have been risking only—only—50,000 lives. But would even one more Allied death have been worth not dropping the bomb, in the minds of the president and his advisors, after six years of the worst fighting in the history of the human race?

Imagine if Truman had decided to hold back. The war ends, with yet more massive bloodshed, probably at some point in 1946. Truman at some point reveals the existence of the bomb, and the president of the United States explains to thousands of grieving parents and wounded veterans that he did not use it because he thought it was too horrible to drop on the enemy, even after a sneak attack, a global war, hundreds of thousands of Americans killed and wounded in two theaters, and years of ghastly firebombing. Seventy years later, we would likely be writing retrospectives on “the impeachment of Harry S. Truman.”

Finally, what about the argument, imbued (wrongly) in several generations of students of international relations, that Truman only dropped the bomb in order to impress the Soviets and establish U.S. dominance in the coming Cold War?

There’s no doubt that the Americans wanted the war over before the Soviets could enter Japan—ironically, something we ourselves had asked them to do when we thought we would have to invade. From the victory at Stalingrad in 1943 onward, U.S. leaders (at least those other than the sickly Roosevelt) realized that Stalin’s Soviet Union was not interested in a peaceful world order policed by the great powers. The Americans were in a hurry to force a Japanese surrender, but they had no way of knowing whether that surrender was imminent. Ward Wilson, for one, claims that the Japanese surrendered not because of the bomb but because of the Soviet entry into the Pacific war, but only the most cold-blooded president would have counted on this and held America’s greatest weapon in reserve.

Again, consider the counterfactual. For years after World War II, the Soviets charged that the nuclear attacks on Japan were a warning to the USSR. Imagine, however, a world in which America held back the bomb, and allowed the Soviets to fight their way through Japan, taking huge casualties along the way. The speeches Stalin and his successors would have given during the Cold War write themselves: “America allowed Soviet soldiers to spill their blood on the beaches of Japan, while Truman and his criminal gang protected the secret of their ultimate weapon. We shall never forget, nor forgive, this squandering of Soviet lives…”

In reality, of course, as soon as the bomb was tested, Truman told Stalin that America had a weapon of great power nearing completion. Stalin, well informed due to his spy networks inside the U.S. nuclear effort, knew exactly what Truman meant, and he told the U.S. president to make good use of this new addition to the Allied arsenal. Both leaders were being cagey, but it was really the only conversation these two men, leading huge armies against the Axis, could have had in 1945 that would have made any sense.

In the 1995 film Crimson Tide, Gene Hackman played a Navy captain whose views are no doubt how critics see American thinking about the decision to use nuclear weapons. “If someone asked me if we should bomb Japan,” he opines while enjoying cigar in the wardroom, “a simple ‘Yes.’ By all means, sir, drop that [expletive]. Twice.”

The actual decision to drop the bomb was not nearly as casual as “a simple yes.” Critics of the decision to use the “special bomb” in 1945 are judging men born in the 19th century by the standards of the 21st. Had Truman and his commanders shrunk from doing everything possible to force the war to its end, the American people would never have forgiven them. This judgment no doubt mattered more to these leaders than the disapproval of academic historians a half century later, and rightly so.