omorrow will mark the anniversary of one of the most morally contentious events of the 20th century, the atomic bombing of Hiroshima. And after 58 years, there's an emerging consensus: we Americans have blood on our hands.

There has been a chorus here and abroad that the U.S. has little moral standing on the issue of weapons of mass destruction because we were the first to use the atomic bomb. As Nelson Mandela said of Americans in a speech on Jan. 31, "Because they decided to kill innocent people in Japan, who are still suffering from that, who are they now to pretend that they are the policeman of the world?"

The traditional American position, that our intention in dropping the bombs on Hiroshima and then Nagasaki was to end the war early and save lives, has been poked full of holes. Revisionist historians like Gar Alperovitz argue persuasively that Washington believed the bombing militarily unnecessary (except to establish American primacy in the postwar order) because, as the U.S. Strategic Bombing Survey put it in 1946, "in all probability" Japan would have surrendered even without the atomic bombs.

Yet this emerging consensus is, I think, profoundly mistaken.

While American scholarship has undercut the U.S. moral position, Japanese historical research has bolstered it. The Japanese scholarship, by historians like Sadao Asada of Doshisha University in Kyoto, notes that Japanese wartime leaders who favored surrender saw their salvation in the atomic bombing. The Japanese military was steadfastly refusing to give up, so the peace faction seized upon the bombing as a new argument to force surrender.

"We of the peace party were assisted by the atomic bomb in our endeavor to end the war," Koichi Kido, one of Emperor Hirohito's closest aides, said later.

Wartime records and memoirs show that the emperor and some of his aides wanted to end the war by summer 1945. But they were vacillating and couldn't prevail over a military that was determined to keep going even if that meant, as a navy official urged at one meeting, "sacrificing 20 million Japanese lives."

The atomic bombings broke this political stalemate and were thus described by Mitsumasa Yonai, the navy minister at the time, as a "gift from heaven."

Without the atomic bombings, Japan would have continued fighting by inertia. This would have meant more firebombing of Japanese cities and a ground invasion, planned for November 1945, of the main Japanese islands. The fighting over the small, sparsely populated islands of Okinawa had killed 14,000 Americans and 200,000 Japanese, and in the main islands the toll would have run into the millions.

"The atomic bomb was a golden opportunity given by heaven for Japan to end the war," Hisatsune Sakomizu, the chief cabinet secretary in 1945, said later.

Some argue that the U.S. could have demonstrated the bomb on an uninhabited island, or could have encouraged surrender by promising that Japan could keep its emperor. Yes, perhaps, and we should have tried. We could also have waited longer before dropping the second bomb, on Nagasaki.

But, sadly, the record suggests that restraint would not have worked. The Japanese military ferociously resisted surrender even after two atomic bombings on major cities, even after Soviet entry into the war, even when it expected another atomic bomb — on Tokyo.

One of the great tales of World War II concerns an American fighter pilot named Marcus McDilda who was shot down on Aug. 8 and brutally interrogated about the atomic bombs. He knew nothing, but under torture he "confessed" that the U.S. had 100 more nuclear weapons and planned to destroy Tokyo "in the next few days." The war minister informed the cabinet of this grim news — but still adamantly opposed surrender. In the aftermath of the atomic bombing, the emperor and peace faction finally insisted on surrender and were able to prevail.

It feels unseemly to defend the vaporizing of two cities, events that are regarded in some quarters as among the most monstrous acts of the 20th century. But we owe it to history to appreciate that the greatest tragedy of Hiroshima was not that so many people were incinerated in an instant, but that in a complex and brutal world, the alternatives were worse.