Eminiar VII and Vendikar had waged a five-hundred-year war by computer simulation, with citizens counted as casualties reporting to be killed, until Kirk destroyed the war computers.
The Enterprise carried Ambassador Robert Fox to Eminiar VII to establish relations and found a planet locked in a war with its neighbor Vendikar that had lasted about five centuries. The two sides fought only with computers. Simulated attacks were scored, and people listed as dead were required to report to disintegration chambers, so the war never destroyed buildings or culture.
When the Enterprise was declared a casualty in orbit, the Eminians demanded that the crew beam down to die. Kirk refused, destroyed the war computers and told both sides they now faced real war unless they made peace. Fox began negotiations between the two worlds.