What if Truman hadn’t used the bomb?

Would humanity be better off? Or extinct?

In the summer of 1945 Harry Truman confronted one of the most momentous decisions ever made by a national leader in human history. America’s scientists and engineers had just produced a weapon unlike any other before it, a weapon that could annihilate cities and hundreds of thousands of people in the blink of an eye. Should he use the atom bomb against Japan? Or not?

If Truman ordered the bomb used against Japan, he could hope to end the Pacific war swiftly, obviating an invasion of Japan’s home islands. Many thousands of Japanese would die in the bombing. No one knew how many thousands. No weapon like this had ever been used against a city.

If Truman did not use the bomb, the invasion would go ahead. Many thousands of Americans would die, and many thousands of Japanese. No one knew how many. No invasion quite like this had ever taken place. Very possibly more Japanese would die in an invasion than would die from the bomb.

Truman ordered the bomb used against Hiroshima. When Japan rejected Truman’s call to surrender, he ordered a second atom bomb used against Nagasaki. Thereupon Japan surrendered, and the war ended.

What if Truman had not used the bomb?

The Pacific war still would have ended in Japan’s defeat. The only question was how long that defeat would have taken. Conceivably Japan would have surrendered before the planned invasion commenced. But that seems improbable, given the stubbornness with which Japan had fought to defend even small islands it occupied in the Pacific. Most likely the war fighting would have continued into 1946, with hundreds of thousands of casualties.

The bomb was a closely held secret before it was used against Japan. But thousands of people were involved in its development, and if Truman had refused to order its use and tens of thousands of American soldiers and seamen had died as a result, someone would have leaked the story to the press. Truman himself said he thought he would have been impeached if he hadn’t used the bomb and the war had continued to take a large toll of American lives. He probably was right.

The use of the bomb carried humanity across the threshold into the nuclear age, an era in which humans possess the power to destroy much or all of our species, and many other species too. Many, perhaps most, retrospective commentators have lamented this transition. More than a few condemn Truman for giving the fateful order.

But what if he hadn’t? The bomb would still have existed. The Soviets knew it existed, for they had spies inside the Manhattan Project. Their presence explained why Stalin was unimpressed when Truman told him at the Potsdam conference that America had successfully tested an important new weapon. Truman was puzzled that Stalin didn’t ask for details. Stalin already had the details.

No one knew how big a deal the bomb was. The New Mexico test raised a lot of dust, but the desert still looked like the desert after the blast. This was one reason Truman rejected the idea of demonstrating to the Japanese the use of the bomb on an uninhabited island in the Pacific. They might very well not have been impressed.

Possibly if the United States had not used the bomb, no other country would have developed its own version. But as the Cold War unfolded, and the United States and the Soviet Union went from being allies to being rivals, Stalin would have had a strong incentive to do what he did in the actual event, namely build a Soviet a-bomb, with intelligence gleaned by those Soviet spies. Presumably the Soviets would have felt obliged to test their device, and American sensors would have detected the test, as they actually did in 1949.

The deeper question is whether the use of the bomb made subsequent use less likely or more likely. On one hand, the American use worked marvelously well, compelling Japan’s surrender within days rather than the months it might otherwise have taken.

On the other hand, it caused a moral revulsion against these horrible new weapons. The destruction at Hiroshima and Nagasaki was less than the destruction at Tokyo by conventional weapons. But Tokyo's destruction required hundreds of planes and thousands of bombs. Hiroshima and Nagasaki were obliterated by one bomb each. Perhaps humans were simply not supposed to wield such power over themselves and their planet.

The moral revulsion grew more powerful with time. In the immediate aftermath of Japan's surrender, most Americans were relieved and indeed happy that Truman had used the bomb. The feeling was understandably greatest among American soldiers who had returned to America from Europe after the defeat of Germany and were preparing to ship out to the Pacific.

Yet as happens with historical events, Japan's surrender came to seem inevitable. Many Americans, and many more people in other countries, began to think Truman had erred, even committed a war crime, in using the bomb unnecessarily, as the use often appeared in hindsight.

Absent Truman's decision, there would have been no moral revulsion. There might have been an arms race. It might well have escalated from fission bombs to fusion bombs—from A-bombs to H-bombs—as it actually did after the Soviet atom test. By the 1960s, the two sides might have had sufficient arsenals to seriously threaten human civilization.

Suppose the Cuban missile crisis of 1962 had occurred without a nuclear weapon ever having been used. With no memory of Hiroshima and Nagasaki, would Kennedy and Khrushchev have been less careful? When Truman dropped the bomb in 1945, he didn't have to worry about enemy retaliation in kind. If either Kennedy or Khrushchev, lacking knowledge of what nuclear weapons could do against a real target, had given the launch order, the other would have felt compelled to retaliate, as Kennedy threatened publicly to do.

No important weapons system that humans have devised has ever not been used in war. As terrible as was the first use of nuclear weapons in war, by the United States against Japan, our species might be fortunate that it occurred when it did. Had it not occurred until the power and number of nukes had increased many-fold, and until the other side also had nukes . . . well, we might not be here in 2025 to ponder the matter.