When Barack Obama goes to Hiroshima on May 27, becoming the first sitting U.S. president to visit the site of the world’s first nuclear attack, he will not apologize on behalf of his country for carrying out that strike 71 years ago. He will neither question the decision to drop bombs on two Japanese cities, nor dwell on its results: the deaths of more than 200,000 people and the dawn of the atomic age. But he will affirm America’s “moral responsibility,” as the only nation to have used nuclear weapons, to prevent their future use. He will recognize the painful past, but he won’t revisit it. When it’s all over, we still won’t know whether or not he thinks there’s something about the atomic bombings to be sorry for.

But why is expressing remorse such a big deal in the first place? Setting aside the arguments for and against the bombings of Hiroshima and Nagasaki, what makes apologizing different for countries than for people? When I put this question to Jennifer Lind, a professor of government at Dartmouth College who has studied these issues extensively, she gave me a one-word answer: “politics.”

She then elaborated: “I don’t have politics. If I was a complete jerk to my husband, then I tell my husband, ‘You know, I was thinking about it this morning. I was a jerk. I’m really sorry.’ And that’s the end of it, because I’ve decided I have a story of what happened and that’s my story and I move on. But if we’re in a collective entity where there are different groups involved and we’re speaking on their behalf, and we’re in a world, by the way, where a lot of people have this idea about the kind of image we need to project to the world, then it gets a whole lot more complicated.”

This is especially true with the Hiroshima bombing, where the competing stories about what happened are so morally complex. Nevertheless, political apologies do occur. The political scientist Graham Dodds has compiled a long list of them—one that begins with Holy Roman Emperor Henry IV, in 1077, expressing remorse for clashing with Pope Gregory VII by standing barefoot in the snow and begging for a meeting with His Holiness. (Imagine what conservatives who claim Obama apologizes for America too much would say about poor, probably frostbitten Henry.) The list also includes several German leaders offering acts of contrition and reparations for the Holocaust and other Nazi atrocities.

Just last week, Canadian Prime Minister Justin Trudeau apologized in Parliament for an incident more than 100 years ago in which Canadian authorities turned away a ship carrying hundreds of South Asian immigrants. Reflecting on Trudeau’s gesture, the CBC’s Neil Macdonald wrote that in recent years, Canadian politicians have been far more willing than their American counterparts to issue official apologies—for things like the internment of Japanese Canadians during World War II and a scheme that removed indigenous children from their communities. Still, Macdonald conceded, Trudeau’s “apology didn’t cost anyone anything … and has no effect on any government policy. It was just a nice thing to do.”

Lind compared Trudeau’s statement to President Bill Clinton’s apology for America’s failure to intervene in the Rwandan Genocide. Clinton was saying sorry for inaction rather than action, she said, and there was no American constituency to be offended by his expression of regret. “It’s a really big difference if you have a generation of people who have been worshipping war heroes and you suddenly say, ‘The thing they did, we should not have done. And it was wrong,’” she explained, in reference to the atomic bombings.

Germany’s various apologies for the crimes of the Nazis, Lind added, are the shining exception in international affairs, not the rule: “The world we live in is one in which countries routinely whitewash their past violence. They routinely even lie about their past violence. They sometimes glorify their past violence.”

Lind’s research indicates, in cases of war between countries, that denying past wrongs seriously hinders future reconciliation; as a case in point, she noted the bitter disputes between Japan and South Korea over Korean “comfort women” forced into sexual slavery during World War II. But Lind has found that apologies and reparations for those wrongs can be damaging as well, since such actions are likely to polarize people within those countries. The best approach, she says, is recognizing and remembering wrongs in ways that unify rather than divide—that emphasize shared suffering, not perpetrators and victims.

In her 1997 study of Japan’s struggle to account for its wartime actions, the University of Chicago scholar Norma Field defined the “ideal historical apology” as a “verbal apology [that] must be in part a statement of the truth of what happened and in part an expression of penitent regret, and [that] must be accompanied by material compensation.” Lind, by contrast, argues that former enemies can often improve relations merely by taking the first step: acknowledging the truth of what happened.

Apologies tend to be controversial domestically because of ideological differences over how to strengthen national identity, Lind said, citing liberals and conservatives in the United States as an example: “Liberals have this idea that the way to be a strong nation is to be transparent about the past, and to be self-critical, and to constantly question your leaders, and constantly ask, ‘Are we living up to our own values?’ And so this kind of historical reckoning with the past [that Obama is undertaking in Hiroshima]—they love that. … And it falls in line with this idea of a cosmopolitan world where everyone’s connected and we need to be nurturing all of these relationships and showing respect.”

Conservatives, meanwhile, “say that national strength comes from national unity, and national unity is best served by instilling pride in people, and pride comes from remembering the really great things that we’ve done, and remembering what’s different and great about America. … And so they would say, ‘What are you doing talking about all the people we killed? Why aren’t you celebrating that we brought democracy to Japan? Why aren’t you celebrating all the people that we freed from Japanese tyranny and Japanese torture and atrocities?’”

These divisions were on display in 1995, the 50th anniversary of the atomic bombings, when veterans organizations and members of Congress condemned a planned Smithsonian exhibit of a section of the Enola Gay, the plane that bombed Hiroshima. Critics took issue with parts of the display that, in their view, characterized the Americans as aggressors and the Japanese as victims, and challenged the dominant American narrative that the atomic bombings were necessary to force Japan’s surrender, avoid a bloodier invasion, and end both a savage world war and a brutal Japanese military campaign in Asia. The exhibit’s script was revised five times, only for the text to ultimately be discarded. All that remained in the display was the Enola Gay and a commemorative plaque.

At the time, Mark Pollock, a professor at Loyola University Chicago, argued that the schism between World War II veterans and museum curators was the product not only of differences between conservatives and liberals, but also of generational dynamics.

“[My father] felt he’d never come out of the war alive, that I would never have been born, without the bomb,” he told the Chicago Tribune. “I started college in 1971, when a lot of American history was being seen through the prism of Vietnam. My father saw history through the prism of World War II—that America fights good wars."

Politics. Everyone has their own story.

The fuselage of the Enola Gay, on display at the Smithsonian Air and Space Museum in 1995 (Reuters)

The vast majority of Japanese don’t think the atomic bombings were justified, and that belief has only become more widespread over time. But Japanese leaders have not demanded that the U.S. government apologize for the attacks, in part because they don’t want to jeopardize the flourishing U.S.-Japanese alliance or encourage calls for Japan to apologize for its own wartime aggression. (The Japanese government hasn’t explicitly said sorry for the Pearl Harbor attacks, though Prime Minister Shinzo Abe did express “deep repentance” during a recent visit to Congress and the World War II memorial in Washington.)  

This lack of a demand from the Japanese, Lind argues, has created the friendly space in which a visit like Obama’s can take place—and in which the two countries can adopt a common narrative about the atomic bombings. They can’t agree on the wisdom of those bombings, or on celebrating Japan’s defeat in the Second World War, or on who the good and bad guys were, but they can both endorse a mission to stop the spread of nuclear weapons. That’s why Obama will focus on nuclear non-proliferation when he visits Hiroshima.

Lind compared the situation to the way in which American and European leaders, including German leaders, now gather in Normandy to commemorate the Allied invasion of Nazi-occupied France. All the leaders tell the same story, which, in Lind’s words, goes something like this: “‘This was a terrible war, Germany was liberated from tyranny, Europe has committed itself to European unity and the taming of anarchy, and thank goodness.’”

“It’s really amazing that the Germans can sign on to that narrative—like, ‘Yay, we were defeated,’” Lind continued. “That is extraordinary.” (As my colleague James Fallows suggests, Germany’s exceptional apologies and reckoning with its Nazi past may stem from the fact that the Holocaust was such an unambiguous evil.)

In Hiroshima, Obama will try to advance a narrative that bypasses the rigid, decades-old debate over the bombings. “For most Japanese, Obama’s visit actually fits with the Japanese story about the bomb—that the atomic bomb gave Japan its postwar mission for peace,” Carol Gluck, a professor of Japanese history at Columbia University, told the radio show On the Media last week. “Now, the story in the United States is very different—that the atomic bomb ended the war and saved American lives. So the Japanese bomb story begins in 1945 and goes forward in the mission for peace. The American bomb story ends in ’45. Those are two separate stories. They will not cross. And the president’s position that the lesson of the past is for a non-nuclear future, it’s almost like a third story.” The logic, it seems, is that Hiroshima’s dark, disputed history is a dead end. So you pivot from the past to the future—and find a way to tell a different story.