Just as Hiroshima has become the symbol of the horrors of nuclear war and the essentialness of peace, the visit of the first sitting U.S. president to that city was laden with symbolism, including about the ironies of human action. As Barack Obama put it, when the United States carried out history’s first nuclear attack by dropping a bomb, “a flash of light and a wall of fire destroyed a city and demonstrated that mankind possessed the means to destroy itself.”

Two questions, however, remain unanswered to this day: Why did the U.S. carry out the twin atomic attacks when Japan appeared to be on the verge of unconditionally surrendering? And why was the second bomb dropped just three days after the first, before Japan had time to fully grasp the strategic implications of the first nuclear attack?

Months before the nuclear bombings, the defeat of Japan was a foregone conclusion. Japan’s navy and air force had been destroyed and its economy devastated by a U.S. naval blockade and relentless American firebombing raids.

During his Hiroshima visit, Obama called for “a future in which Hiroshima and Nagasaki are known not as the dawn of atomic warfare but as the start of our own moral awakening.” But can there be a moral awakening when almost every nuclear power today is expanding or upgrading its arsenal, thus increasing the risk of nuclear use, either by accident or design?

Obama has himself highlighted the yawning gap between rhetoric and reality. In Hiroshima, reprising his famous words of 2009 in Prague, Obama said that “among those nations like my own that hold nuclear stockpiles, we must have the courage to escape the logic of fear and pursue a world without them.” But at home, he has quietly pursued an extensive expansion of the U.S. nuclear arsenal. Under him, the U.S. is spending about $355 billion as part of a 10-year plan to upgrade its nuclear armory.

Almost 71 years after the nuclear incineration of Hiroshima and Nagasaki and more than a generation after the end of the Cold War, nuclear weapons still underpin the security policies of the world’s most powerful states. Indeed, the composition of the United Nations Security Council’s permanent membership suggests that international political power is coterminous with intercontinental-range nuclear-weapons power.

There can be no moral awakening without jettisoning the political-military thinking that sanctioned the nuclear attacks on Hiroshima and Nagasaki, leaving as many as 220,000 people — mostly civilians — dead. As Hiroshima and Nagasaki lay in ruins, President Harry Truman sent a team of military engineers, fire experts and photographers to the scene to analyze the death and destruction wrought by the twin attacks. The team reported “an unprecedented casualty rate” in Hiroshima, with 30 percent of the population killed and another 30 percent seriously injured.

The nuclear attack on Nagasaki generated a higher blast yield but produced a smaller area of complete devastation and lower casualties because, unlike Hiroshima’s flat terrain and circular shape, Nagasaki is a city with large hills and twin valleys. The second attack killed about 74,000 people, about half as many as those who died in the Hiroshima bombing. A city’s terrain and layout, the U.S. team’s report stated, must be considered “in evaluating the effectiveness” of nuclear bombing.

Even if one accepts Truman’s claim that the Hiroshima bombing was necessary to force Japan’s surrender and end the war without a full-scale U.S. invasion, what was the rationale for his action in nuking Nagasaki just three days later on Aug. 9, before Japan had time to surrender?

As the U.S. team’s report stated, Nagasaki was totally unprepared for the nuclear bombing, although “vague references to the Hiroshima disaster had appeared in the newspaper of Aug. 8.”

Decades later, there is still no debate in the U.S. on the moral or military calculus for bombing Nagasaki. No plausible explanation has been proffered for the attack.

After Hiroshima was nuked on Aug. 6, Russia took advantage of the situation by attacking Japan on Aug. 8, although its official declaration of war came a day later. Hours after news of Russia’s invasion of Sakhalin Island reached Tokyo, the Supreme War Guidance Council met to discuss Japan’s unconditional surrender. The nuclear bomb on Nagasaki was dropped as Soviet forces were overwhelming Japanese positions in Manchuria and Japan appeared set to surrender to the Allied powers.

Indeed, according to the U.S. team’s report, the “decision to seek ways and means to terminate the war — influenced in part by knowledge of the low state of popular morale — had been taken in May 1945 by the Supreme War Guidance Council.” This would suggest that even the nuclear bombing of Hiroshima was needless.

In the days before the Hiroshima and Nagasaki bombings, the only question facing Japan was when to unconditionally surrender under the terms of the July 26 Potsdam Declaration. The signals the Japanese were sending that they were prepared to surrender were missed or ignored by the U.S. The surrender was eventually announced by Emperor Hirohito on Aug. 15 after U.S. assurances on the Emperor’s continued role — assurances that were not provided earlier, as American scholar Gar Alperovitz has pointed out — which possibly could have ended the war without the atomic bombs being used.

In truth, Nagasaki’s nuclear incineration had no military imperative. If there was any rationale, it was technical or strategic in nature — to demonstrate the power of the world’s first plutonium bomb. The bomb that reduced Hiroshima to ashes was an untested uranium bomb, code-named “Little Boy,” with Truman applauding the bomb’s success as “the greatest achievement of organized science in history.” The bomb used in the Nagasaki attack was an implosion-type plutonium bomb. Code-named “Fat Man,” it had been secretly tested in the New Mexico desert on July 16, a development that paved the way for the Postdam ultimatum to Japan.

Indeed, Truman intentionally delayed his Potsdam meeting with Soviet strongman Josef Stalin until after the testing of the new weapon. Truman wanted the power of the new weapon to end the war in the Pacific, rather than the Soviet Union invading Japan and inflicting a decisive blow to force its surrender. Anxious not to let the Soviet Union gain a major foothold in the Asia-Pacific region, he sought to persuade Stalin at Postdam to delay the invasion.

Days later when Hiroshima was destroyed, Truman broke the news to his shipmates aboard the USS Augusta, saying, “The experiment has been an overwhelming success.” The Nagasaki bombing was his second nuclear “experiment.” The geopolitical logic of the nuclear bombings was to establish U.S. primacy in the postwar order.

American author Kurt Vonnegut, best known for his World War II satirical novel “Slaughterhouse-Five,” called the Nagasaki bombing the “most racist, nastiest act” of the U.S. after the enslavement of blacks. And the chief prosecutor at the Nuremberg trials, Telford Taylor, once described the Nagasaki bombing as a war crime, saying: “The rights and wrongs of Hiroshima are debatable, but I have never heard a plausible justification of Nagasaki.”

Actually, the U.S. plan was to drop the plutonium bomb on Kokura (present-day Kitakyushu). But Kokura was under a heavy cloud blanket on Aug. 9, so the B-29 bomber was diverted to a larger city, Nagasaki, Japan’s gateway to the world. Nagasaki, Japan’s oldest and densest stronghold of Roman Catholicism, was paradoxically destroyed by a predominantly Christian America.

Dropping the more powerful plutonium bomb on a large civilian population center appeared to matter more to those in charge of the “experiment” than which particular city they targeted. Indeed, brushing aside the suggestion of Army Chief of Staff Gen. George C. Marshall for non-urban target selection, the atomic “hit” list comprised important cities.

Japan became something of a guinea pig as the U.S. sought to demonstrate to the world, particularly to the Soviet Union, that it had awesome destructive power at its disposal. After Adolf Hitler, who symbolized the most potent military threat to the Allied powers, committed suicide in April 1945, just days after Truman took office, Japan became the test site for demonstration of America’s newborn nuclear might.

The use of a technological discovery to incinerate Hiroshima and Nagasaki was made possible by a widely prevalent political-military culture at that time that regarded civilian massacres as a legitimate tool of warfare. All sides engaged in mass killings in World War II, in which nearly 60 million people died.

Against this background, no warning was given to the residents of Hiroshima or Nagasaki before unleashing a nuclear holocaust. Nor did Truman give Japan a firm deadline to surrender before rushing into a second nuclear attack.

History is written by the victors, and the vanquishers are rarely burdened by the guilt of their actions. Still, Hiroshima and Nagasaki will remain a burden on American conscience — Hiroshima because it was the world’s first atomic bombing, setting a precedent, and Nagasaki because it was a blatantly wanton act. Obama’s visit to the Hiroshima memorial should be seen in this light. He made no apology, yet he stated expressively: “We come to ponder a terrible force.”

Nuclear arms remain the toxic fruit of a technology that destroyed Hiroshima and Nagasaki. World War II reached its savage end in Hiroshima and Nagasaki only to spawn the dawn of a dangerous nuclear age. And the last strike of the world war, Nagasaki, became the opening shot of a new Cold War.

Nuclear-deterrence strategies still rely on targeting civilian and industrial centers. In fact, a wary U.S., a rising China and a declining Russia are currently developing a new generation of smaller, more effective nukes that threaten to increase nuclear-use risks.

Ominously, the world today has a treaty (although not in force as yet) that bans all nuclear testing, but no treaty to outlaw the use of nuclear weapons. In other words, those that are party to the Comprehensive Test Ban Treaty are prohibited from testing a nuclear weapon at home but remain legally unfettered to test the weapon by dropping it over some other state. The option of “doing a Hiroshima” on an adversary with an untested weapon must be foreclosed.

Brahma Chellaney, a geostrategist and author, is a long-standing contributor to The Japan Times.