No, I think he is talking about the Vulcan/Romulan schism which have been or seemed pretty violent which may have been the actual or not conquering that he is talking about. There is definitely a story there.
How about that alien race that was referred to that had the most sublime thoughts in the galaxy. Can't remember their name, but they seemed interesting.
What would McCoy know about the Vulcan/Romulan schism in season one? In "Balance of Terror" allegedly nobody knows what Romulans look like. So allegedly nobody knows that Romulans are a Vulcan offshoot until "Balance of Terror". So if McCoy ever learned anything about the ancestors of the Romulans in his Vulcan history class (if he ever took one) he wouldn't have heard them named as Romulans but as something else.
And remember that when Spock comments on the resemblance between Romulans and Vulcans he didn't say: "Aha! Those must be the ones who separated from Vulcan 2,455 years ago." Instead he said that it was likely that Romulans are some group descended from Vulcans. Obviously Spock didn't know enough to teach any history of the Romulan-Vulcan separation. He just speculated that Romulans were descended from Vulcans.
Which episode, "Balance of Terror" or "Conscience of the King" happens earlier? "Balance of Terror" was produced 9th, on July 20 to 28, 1966, and was broadcast 14th, on 15 December 1966, and has a beginning stardate of 1709.1. "Conscience of the King" was the 13th episode produced, on September 13 to 21, and the 13th episode broadcast, on 8 December 1966, and has a beginning stardate of 2817.6.
So "Balance of Terror" was probably before "Consicnce of the King", but not certainly. And even if "Balance of Terror" was before, would there be time to uncover the story of the separation vet between the Vulcans and the Romulans, and for Spock to give a lecture on that history on the ships educational channel?