The world is marking today President Truman’s decision to drop an atomic bomb in 1945. Second guessing abounds, but it stands up as the option that ended the war with the least loss of life.

The United Nations secretary general, Antonio Guterres, traveled to Hiroshima for a ceremony intended to “commemorate all victims of World War II.”

This moral equivalence dismisses that Imperial Japan, like their Nazi allies, launched a genocidal war and were “repaid many fold,” as Truman said in his announcement, with the strike on the Hiroshima “army base.”

While America and Japan have built ties of affection across eight decades, the situation was different after they attacked our Pearl Harbor even as agents of both nations were negotiating.

As December 7 faded from living memory, a conventional wisdom formed that Tokyo wanted to surrender and the attack was pointless — even racist — cruelty.

This myth was refuted in 2008. A diary of the country’s wartime leader, Hideki Tojo, documented his aim to ignore the atomic attacks, sticking to the Bushido code forbidding capitulation.

With the Americans closing in, the Empire had a slogan: “The sooner the Americans come, the better — one hundred million die proudly!”

This fanaticism puts the lie to another myth, that staging a fireworks show off the coast with a bomb — America had only two on hand — Japan would have thrown in the towel.

In reality, Tojo hoped for “Ketsu-Go,” or “decisive battle,” to earn an armistice; then, like Germany after World War I, a Hitler might continue the fight for the master race. 

He also instituted a policy summarized as “there are no civilians in Japan,” training everyone down to the youngest child to kill Americans. His regime saw other races as less than human, just like the Nazis.

This was demonstrated in the Bataan Death March, Rape of Nanking, and atrocities such as cannibalism — sometimes cutting strips off civilians while they were still alive.

Even after the bombings enabled Emperor Hirohito to assert control, Japanese soldiers beheaded more than a dozen prisoners of war.

The bomb saved thousands from that fate, Tojo having ordered the execution of all foreigners the moment GI boots hit Japanese soil.

And let’s not forget the tens of thousands of Chinese and other allies dying daily under occupation. The Rising Sun had to be stopped. Fast.

As for the myth that Truman dropped the bomb to warn the Soviet Union, spies had told their dictator, Joseph Stalin, about the Trinity test before Truman did.

Despite these facts, Monday Morning quarterbacks have been condemning Truman ever since VJ Day. President Eisenhower’s response to those who criticized him for not pressing on to Berlin offers an effective rebuttal.

“None of these brave men of 1952,” he said of those armchair critics, “have yet offered to go out and pick out the 10,000 American mothers whose sons should have made the sacrifice…” 

Has anyone offered to choose the mothers of the estimated 1 million Americans who would have died or been maimed to subdue the Home Islands in Operation Downfall?

Many people reading this would not have been born had their grandfathers been thrown into “Okinawa from one end of Japan to the other,” as Truman foresaw it.

In her book “The Jersey Brothers,” Sally Mott Freeman describers her father briefing Truman on the staggering casualty projections. “Grim as it was to drop the bomb,” she told me, “it saved American and Japanese lives.”

The photos of Hiroshima’s aftermath serve as a warning about the costs of going to war, but the bomb remains — as professor of history at Notre Dame, Father Wilson Miscamble, calls it — “the least awful of the options available.”

Jeffrey F. Frank writes in “The Trials of Harry S. Truman,” “As a practical matter,” Truman’s decision to drop the bomb “had been made for him.” And as the Sun said in 2016, the deaths at Hiroshima “came in consequence of Japan’s own tyranny.”