“Stuff happens,” Donald Rumsfeld infamously said to explain why some of his plans in Iraq went awry. But it does not just happen by chance — rather, stuff happens because of conscious, deliberately executed decisions. And sometimes it happens when a decision is made by doing nothing.

The personalities, the interests and the considerations that propelled the United States’ decision to use the atomic bomb in August 1945 are parts of an interlocking puzzle. The historical reconstruction of events reveals a seemingly inexorable decision to use the weapon. We had made a bomb and successfully tested it in July, and the scientists, generals, politicians and civilians caught up in events readily supplied the accelerating momentum to a decision: “We must use it.” That inexorable force in fact found no resistance among civilian decision-makers anxious to justify the expenditures of unprecedented sums of money to develop a weapon designed to end the war.

The historical narrative of the decision to use the bomb largely derives from the recollections and rationales of President Harry Truman and his civilian and military advisers. For them, the stark choice came down to drop the bomb or sustain a “million” American casualties (with apparently no effort to consider and realize the potential for Japanese civilian casualties) if the planned invasion had been launched. A small number of scientists raised ethical and moral considerations, but their influence was of no immediate consequence.

President Truman fashioned himself as a decisive man who easily and readily made the decision. “It isn’t polls or public opinion of the moment that counts,” he said in 1954. “It is right and wrong and leadership — men with fortitude, honesty, and a belief in the right that makes epochs in the history of the world.” So Truman described himself and conducted himself as president, and it is how he has generally been perceived.

Later, at his presidential library in Independence, Mo., the president conducted mock press conferences with tour groups, largely composed of schoolchildren, as long as his heath permitted. Invariably, visitors would ask, “Mr. President, what was your hardest decision?” With no hesitation, he barked back, “Korea.” “But Mr. President, what about the atomic bomb?” “Atomic bomb? I used it like I would have used any artillery piece.” Truman’s defensiveness was palpable.

Were his options so simple, so limited, so stark, and as obvious as he said? Truman learned of the bomb when aides informed him of the successful atomic explosion at Alamogordo, N.M., on July 18. The president and Secretary of War Henry Stimson, who oversaw the wartime Manhattan Project, soon agreed that the bomb would be used against Japan.

Nevertheless, Truman recorded his doubts, his hesitation and his alternatives, at least before Alamogordo. One day earlier, he wrote in his diary: “I have to decide Japanese strategy — shall we invade Japan proper or shall we bomb and blockade? That is my hardest decision to date. But I’ll make it when I have all the facts.” The successful test raised a wholly new fact.

We now realize how effectively the aerial bombardment and naval blockade had thwarted the Japanese military capacity. But did — or could — Truman have all the statistical evidence compiled since the end of the war? The claims of triumphant American air and naval commanders offered some clear signs. So, what happened to the option Truman had in mind until Alamogordo? Did the successful test of that day erase the more complicated options he had laid out the day before? Apparently.

Gen. Curtis LeMay was well into his career of bombing civilians back to the Stone Age. The Air Force was not yet independent, but as the war neared its end, concepts of strategic bombing accelerated, resulting in the creation of the U.S. Strategic Air Force in the Pacific, with LeMay in command. B-29 firebombing raids, pushed by LeMay, decimated industrial production, with more than 60 cities largely destroyed. The infamous Tokyo fire raids in March killed more than 100,000 Japanese. Additionally, “Operation Starvation” laid down explosive mines in the inland waterways and coastal routes, effectively disrupting Japanese internal shipping.

Japan lost nearly all of the 117,000 troops defending Okinawa in June; after that, kamikaze attacks on American naval vessels abated. American submarines effectively halted all shipping of men and supplies from the remaining Japanese garrisons in Manchuria and Formosa. We had “collateral damage,” as thousands of American POWs were killed in the attacks on Japanese shipping. After the Battle of the Philippine Sea in 1944, the once-formidable Japanese fleet was no more, except for some vessels tethered in home ports. War planners realized the diminished Japanese military and industrial capacity they faced; yet, they persisted in a belief that Japanese civilians would fanatically resist and die for their emperor (“120 million hearts beating as one”), while we would suffer estimated casualties of 1 million. (John Ray Skates in his book “Invasion of Japan” details the invasion plans while recognizing the complete devastation of Japan.)

The aerial assault and the naval blockade kept the Pacific commanders busy, of course. But civilian and military planners simultaneously made final tweaks on the elaborate plans for “Operation Downfall,” the planned invasion of Japan. Those plans, of course, were put on hold, and ultimately shelved altogether.

Discussions of the dropping of the bomb rarely raise the effects and potential of the bombing and naval blockade. Were they sufficient? Would they have brought Japan to surrender? When? Did those advocating such alternatives have any voice in the bureaucratic policy considerations? Unfortunately, this is a typical kind of decision-making process that history usually ignores or obscures.

Determining the evaporation of the choice for maintaining the blockade and conventional bombing to break the Japanese will is an elusive problem. Today, it is common wisdom that Truman had only two simple, stark choices: to use the bomb or invade and suffer a “million” casualties. The options of naval blockade and “conventional” bombing quickly dissolved, and over time they have disappeared. Drift and inertia account in part for some of the flow of events as the decision to use the bomb took on a force of its own, with the tragic results of Hiroshima and Nagasaki.

Stanley Kutler is the author of the “Wars of Watergate” and other writings.