That novella: "The Man Who Ended History: A Documentary" by Ken Liu.
Since I take Jamie's recommendations strongly, I followed his link to Ken Liu's stories and read the story. Jamie had said nothing more about the story, and so I went in with no expectations save the one that this was going to be a good story.
I'm with Jamie. It's one of the most powerful stories I've ever read. I don't think it would give too much away to say that as I read it, I found myself comparing it to my own "Kaddish for the Last Survivor" and feeling that it was so much better. If "Kaddish" was a story of mine you found of interest because of its themes and overall subject matter, you should read Liu's story.