“We come to ponder a terrible force,” President Obama said of his purpose in going to the Hiroshima memorial on Friday, the only sitting American president to do so in the 71 years since the United States dropped the first atomic bomb, killing 140,000 people. He mourned the victims and called for a global “moral awakening” on nuclear weapons. His message would have been all the more powerful had he also announced concrete plans for bringing the world a step closer to his nuclear-free vision.

Visits to war memorials are often fraught, and this one more than most. There were debates about whether Mr. Obama should go at all, whether he should meet survivors of the attacks on Hiroshima and Nagasaki and whether he should apologize for America’s decision to drop the bombs, which ended World War II in the Pacific.

Mr. Obama made no apology and affirmed that Japan was responsible for the war, which “grew out of the same base instinct for domination or conquest that had caused conflicts among the simplest tribes.” That was important, given that Japan’s prime minister, Shinzo Abe, has often sought to rewrite the history, portraying Japan as a victim of the war as well.

As for the future, Mr. Obama said it could be one in which “Hiroshima and Nagasaki are known not as the dawn of atomic warfare, but as the start of our own moral awakening.” Reprising the soaring words of his 2009 speech in Prague, he declared, “We must have the courage to escape the logic of fear and pursue a world without” nuclear weapons, while acknowledging that it is unlikely to happen soon.