Barack Obama called for a world without nuclear weapons as he became the first sitting U.S. president to visit the site of the Hiroshima atomic bombing. Some 140,000 people were killed when the U.S. dropped an atomic bomb on the city on Aug. 6, 1945. A helicopter and motorcade brought Obama to the Hiroshima Peace Park Memorial, where he spent a short time in the site’s museum and then solemnly placed a wreath at the arched monument.

Obama reflected on the day “death fell from the sky and the world was changed,” telling a gathering of survivors and officials that a “wall of fire destroyed a city and demonstrated that mankind possessed the means to destroy itself.”

Mr. Obama did not apologise, instead offering, in a carefully choreographed display, a simple reflection on the horrors of war and his hope the horror of Hiroshima could spark a “moral awakening.” As he and Japanese Prime Minister Shinzo Abe stood near an iconic bombed-out domed building, Mr. Obama acknowledged the devastating toll of war and urged the world to do better.

Mr. Obama’s visit is a moment 71 years in the making. Other American presidents considered coming, but the politics were still too sensitive, the emotions too raw. Jimmy Carter visited as a former President in 1984.