Finding that the Klingons were secretly supplying flintlocks to one faction on the planet Neural, Kirk decided to give the other side equal weapons to keep a balance.
Kirk had surveyed the peaceful planet Neural thirteen years before and befriended Tyree, a leader of the hill people. Returning in 2268, he found the villagers armed with flintlock rifles, far beyond their technology, and the Klingons behind it. After Kirk was bitten by a mugato and Spock was shot, Tyree's wife Nona used a local root to save Kirk.
Kirk concluded that the only answer that could stop the hill people from being wiped out was to give them the same weapons. He compared the situation to the brushfire wars of Earth's 20th century. Nona was killed, and Tyree turned toward vengeance, which troubled Kirk.