Vendikar

Vendikar (or Eminiar III) shared the star Eminiar with the planet that colonized it, Eminiar VII. At some point, the two planets became ruthless enemies. Sometime in the late 18th century, war erupted between the two planets. This war, fought entirely with computers, continued for five hundred years, until Captain Kirk and Ambassador Fox ended it in 2267. (TOS: "A Taste of Armageddon")