I'm sure it was a book, but it could have been a film, or even a video-game plot element. Apologize if I've mixed up any facts – I don't think I've come across this again in the last 20 years!
I read this "book" a long time ago, and a small part of the story refers to the Earth being visited by aliens, who (IIRC) told us that they were disappointed in how we had progressed as a species, and gave humanity the chance to repair their culture…
I believe, they left the Earth and came back after a time to be told that humanity had worked hard and had now declared a full and lasting world-peace and equality. However, the aliens wanted the opposite, they wanted us to be even more vicious to be used as soldiers or something along those lines.
I believe that they then promptly destroyed either the planet or the species!