Seventy-one 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.

Why do we come to this place, to Hiroshima? We come to ponder a terrible force unleashed in a not so distant past. We come to mourn the dead, including over 100,000 in Japanese men, women and children; thousands of Koreans; a dozen Americans held prisoner. Their souls speak to us. They ask us to look inward, to take stock of who we are and what we might become.

It is not the fact of war that sets Hiroshima apart. Artifacts tell us that violent conflict appeared with the very first man. Our early ancestors, having learned to make blades from flint and spears from wood, used these tools not just for hunting, but against their own kind. On every continent, the history of civilization is filled with war, whether driven by scarcity of grain or hunger for gold; compelled by nationalist fervor or religious zeal. Empires have risen and fallen. Peoples have been subjugated and liberated. And at each juncture, innocents have suffered, a countless toll, their names forgotten by time.