HIROSHIMA, Japan — Barack Obama paid tribute today to the “silent cry” of the 140,000 people killed by the world’s first atomic bomb attack and sought to renew attention in his unfulfilled vision of a world without nuclear weapons, as he became the first sitting U.S. president to visit Hiroshima.

“Death fell from the sky and the world was changed,” Obama said, after laying a wreath, closing his eyes and briefly bowing his head before an arched monument in Hiroshima’s Peace Memorial Park that honors those killed on Aug. 6, 1945, when U.S. forces dropped the bomb that ushered in the nuclear age. The bombing, Obama said, “demonstrated that mankind possessed the means to destroy itself.”

Obama did not apologize, instead offering, in a carefully choreographed display, a reflection on the horrors of war and his hope that Hiroshima would be remembered as the beginning of a “moral awakening.” As he and Japanese Prime Minister Shinzo Abe stood near an iconic bombed-out domed building, Obama acknowledged the devastating toll of war and urged the world to do better.

A second atomic bomb was dropped on Nagasaki.

Obama also sought to look forward to the day when there was less danger of nuclear war. He received a Nobel Peace Prize early on in his presidency for his anti-nuclear agenda but has since seen uneven progress.

“We must have the courage to escape the logic of fear and pursue a world without them,” Obama said of nuclear weapons.

Following the remarks, Abe called Obama’s visit courageous and long-awaited. He said it would help the suffering of survivors and echoed the anti-nuclear sentiments.

The visit presented a diplomatic tightrope for a U.S. president trying to make history without ripping open old wounds.

The president has been praised by those who see his visit as a long overdue gesture for two allies ready to bury a troubled past.