story identification - Humans winning an interstellar war against hive-minded aliens due to human nature

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.

Answer

"'In a Good Cause—'", a 1951 novelette by Isaac Asimov, also the answer to this question. Under the title "Ideals Die Hard" it was reprinted in Authentic Science Fiction No. 78, March 1957 which is available at the Internet Archive. Maybe one of these covers will ring a bell. Here is an excerpt from the conversation at the end of the story:

"Merely saying so was not enough. You wanted to force the human governments to unite against them and that notion was politically unrealistic and completely impossible. It wasn't even desirable. Humans are not Diaboli. Among the Diaboli, individual consciousness is low, almost nonexistent. Ours is almost overpowering. They have no such thing as politics; we have nothing else. They can never disagree, can have nothing but a single government. We can never agree; if we had a single island to live on, we would split it in three.

"But our very disagreements are our strength! Your Federalist party used to speak of ancient Greece a great deal once. Do you remember? But your people always missed the point. To be sure, Greece could never unite and was therefore ultimately conquered. But even in her state of disunion, she defeated the gigantic Persian Empire. Why?

"I would like to point out that the Greek city-states over centuries had fought with one another. They were forced to specialize in things military to an extent far beyond the Persians. Even the Persians themselves realized that, and in the last century of their imperial existence, Greek mercenaries formed the most valued parts of their armies.

"The same might be said of the small nation-states of pre-atomic Europe, which in centuries of fighting had advanced their military arts to the point where they could overcome and hold for two hundred years the comparatively gigantic empires of Asia.

"So it is with us. The Diaboli, with vast extents of galactic space, have never fought a war. Their military machine is massive, but untried. In fifty years, only such advances have been made by them as they have been able to copy from the various human navies. Humanity, on the other hand, has competed ferociously in warfare. Each government has raced to keep ahead of its neighbors in military science. They've had to! It was our own disunion that made the terrible race for survival necessary, so that in the end almost any one of us was a match for all the Diaboli, provided only that none of us would fight on their side in a general war.

"It was toward the prevention of such a development that all of Earth's diplomacy has been aimed. Until it was certain that in a war between Earth and the Diaboli, the rest of humanity would be at least neutral, there could be no war, and no union of human governments could be allowed, since the race for military perfection must continue. Once we were sure of neutrality, through the hoax that broke up the conference two years ago, we sought the war, and now we have it."

Wikipedia plot summary:

The story opens with a description of a statue on the grounds of the United Worlds organisation raised to Richard "Dick" Altmayer. It displays a quote and three dates, which correspond to the three days upon which he was arrested for his beliefs. The first is in the year 2755 of the "Atomic Era" (corresponding to 4700 CE in Asimovean chronology).

Altmayer and his friend Geoffrey Stock have opposing positions when conscripted into military service for a war between human-occupied star systems. Stock willingly reports for military duty, whilst Altmayer protests, believing that the various interstellar nations of humanity should be united against the Diaboli, an intelligent non-human race that also occupies several planetary systems in the galaxy.

Over a 45-year period, Stock reaches high military rank and then political office, whilst Altmayer is imprisoned and kept under house arrest several times for his radical idealism. He starts political parties and protest movements, all of which fail to achieve their objectives of uniting humanity.

Ultimately, Altmayer's desire for a united humanity is achieved after a war against the Diaboli. This unity, however, has been realised only through Stock's political manipulations rather than Altmayer's idealistic actions. Stock asks his one-time friend to be one of the delegates from Earth to a peace conference, but realizes that history will not record his own participation in the unification of humanity, but will instead vilify him as a cruel and short-sighted politician.