On August 6, 1945, Americans in a single B-29 bomber dropped the bomb heard 'round the world. Three days later another bomb was dropped.
The bombs were, of course, the two atom bombs then currently in existence. They brought about the end of the war without having to invade Japan, a nation its militarist leaders swore to defend to the last citizen. After the bombings, the thought of oblivion at the hands of such awesome weaponry made sure wiser heads in the Japanese government prevailed, and the war was brought to a close.
My wife and I have had a debate over those bombings for years. She thinks that under no circumstances should nuclear weapons have been dropped on a civilian population. While I agree it was cold-blooded, I argue from the standpoint of the wartime American military and government leadership, appalled by heavy losses of men and equipment invading and occupying island after island in the Pacific in order to secure a foothold for the final assault on Japan. There was a threat that thousands more American men would die in an invasion of Japan.
In 1945, dropping those bombs changed the world. Maybe some saw them as a means to the end of a nasty, costly war, and didn't look down the road decades in the future to imagine what those bombs would mean to future generations.
The contemporary account in Life, August 20, 1945, tells the story of the bombings to readers who had just been through the biggest war in the history of humanity. More often than not, Americans were probably sympathetic to the idea of bombing Japan with the most awful weapons ever built. As long as those weapons were in our hands and not an enemy nation.
The enemy nation got its bombs soon after. It remains, though, that the United States is the only nuclear power (so far) to have deliberately dropped bombs on civilian populations during a time of war.