Obama said that "71 years ago on a bright, cloudless morning, death fell from the sky and the world was changed."
"A flash of light and a wall of fire destroyed a city, and demonstrated that mankind possessed the means to destroy itself," the President added during his address at the site of the first nuclear bombing.
Obama was not expected to apologize for the U.S. action to hasten the end of World War II and he did not during his 20-minute-long remarks.
"Why do we come to this place, to Hiroshima? We come to ponder the terrible forces unleashed in the not so distant past. We come to mourn the dead ... their souls speak to us and ask us to look inward. To take stock of who we are and what we might become."
In the Hiroshima museum's guest book before his speech, the President wrote that he hoped the world will "find the courage, together, to spread peace, and pursue a world without nuclear weapons."