On May 27^th this year Barack Obama had been the first sitting U.S. president to visit Hiroshima. Accompanied by Japanese Prime Minister Shinzo Abe, Obama laid a wreath at the Hiroshima Peace Memorial. We didn’t know what to say, but the White House had emphasized that he will not apologize for the U.S. decision to drop atomic bombs on Hiroshima and Nagasaki in the closing days of World War II. Nor should he.

On August 6^th 1945, Hiroshima was a city of 350.000 well-braced for U.S. bombing raids. Makeshift fire lanes snaked through neighborhoods. Locals built concrete tanks alongside houses and filled them with water — to extinguish fires but also to leap into as lifesaving refuge. That morning, two or three B-29 bombers were spotted, but no one ran for shelters — big bombing raids almost always meant a sky filled with attacking bombers.

Then, at 8:14 a.m., „Little Boy“ fell from the Enola Gay flying at 31.000 feet.

Witness accounts run the gamut, but everyone remembers the blinding flash of light. Schoolgirls saw it through their classroom windows moments before the ceiling crashed down on top of them. In Gerard DeGroot’s book „The Bomb“, middle school student Michiko Yamaoka remembers „a very strong light, a flash“, just as her face ballooned and her body flew into the air.

The Enola Gay’s pilot, Colonel Paul Tibbetts, remembers how „the bright light filled the plane … the whole plane cracked and crinkled from the blast. We turned back to look at Hiroshima. The city was hidden by that awful cloud … mushrooming, terrible and incredibly tall“.

In the inferno that Hiroshima became, scorched, disfigured bodies lay everywhere. Railroad ties caught fire. Thousands died instantly. By December 1945, the death toll reached 140.000, about 40 percent of the city’s population. In the years that followed, radiation took its toll: intestinal bleeding, stillbirths, cataracts, leukemia and other kinds of cancers.

There is hope among Hiroshima’s Japanese that Obama´s visit will revive talk of nuclear disarmament. That’s a reasonable expectation:

Less than three months after taking office in 2009, Obama appeared on a hilltop plaza in Prague and called for „a world without nuclear weapons. … The world must stand together to stop the spread of these weapons“. When it comes to today’s most worrisome nuclear threats, however — nuclear arsenals vulnerable to terrorists or in the hands of rogue states — there is still a good deal of work to do. There are serious questions about whether the West’s nuclear pact with Iran will keep that nation from developing nukes. Another danger: Pakistan’s military continues to beef up its nuclear weapons stockpile in a country ceaselessly grappling with Islamic militancy. And the bizarre regime in North Korea continues to threaten nuclear strikes against its enemies.

The harrowing legacy of Hiroshima and Nagasaki reminds us that blocking nuclear proliferation needs to be a relentlessly urgent priority. That legacy is mankind’s only window into the hell that a nuclear explosion inflicts on innocents. Books on Hiroshima describe the blackened wasteland after the blast: a woman’s charred body, frozen in a running pose, holding tight her baby; bloated corpses floating down the Ota River; other bodies with the floral patterns from their kimonos burned into their skin.

Obama encountered Hiroshima’s grim images when he toured the grounds of the Hiroshima Peace Memorial. The director of the memorial’s museum, Kenji Shiga, recently told the Japan Times that he won’t seek an apology from Obama. He just wanted the president „to face our displays not as someone in power, but as a human being, or a father“.

We whom we are born after this disaster are held to carry the legacy in the future. It cannot be so difficult to abolish nuclear weapons and to clear conflicts verbally or by plebiscite in future. These proposals are not new, they were already made by Woodrow Wilson (14-point rule) after the catastrophe of the beginning last century – World War I. Hundred years later we stay in the same old groove. We should have been more openminded after the twentieth century. In the background a threat: total distruction!