The crew of the USS Exeter died of disease at Omega IV, and their captain, Ronald Tracey, broke the Prime Directive by arming one side in a planetary war.
In 2268 the Enterprise found the USS Exeter in orbit of Omega IV, its crew reduced to crystals by a disease brought back from the planet. Captain Ronald Tracey had survived on the surface and was using phasers to help the Kohms in their war against the Yangs, believing the people held a secret of long life. In fact their long lives were a natural result of the disease.
The Yangs won, and Kirk recognized their sacred banner and texts as versions of the flag and Constitution of the United States. Kirk defeated Tracey in combat, read the text to the Yangs to restore its meaning, and placed Tracey under arrest.