This question already has an answer here:
I read this story in the mid/late 90's, and I believe it was in a Sci-Fi anthology or a magazine (such as Asimov), so it's possibly much older.
Unfortunately, the only details I remember are very generic, so Google searches haven't been terribly helpful; it all centers around a specific scene, which I believe is near the end of the story. Each piece I can remember is a concept which is present in numerous stories/movies/games, which further leads me to believe that this is much older than the 90's.
I remember that humans are at war with a hive-minded alien species, and this species initially stomps human fleets in virtually every battle. Because they're a hive mind, they are perfectly unified in strategy, politics, and scientific research.
At the end, it's revealed that this race is doomed to lose, because it's unified. Humans are constantly fighting, so our strategies quickly adapted to the enemy's, and we were able to rapidly reverse-engineer the aliens' superior technology to use it for ourselves.
I believe it's also revealed that the war was intentionally started by a human organization to give humans a common enemy.
I vaguely remember that all of this is revealed through a single conversation at the end of the story, but that's the extent of my memories on the subject.