For over five hundred years, Vendikar was governed by a planetary government. This government was headed by the Vendikar High Council. There was a direct channel between this council and the High Council of Eminiar, which, by 2267, hadn't been used for centuries. (TOS: "A Taste of Armageddon")
These Eminians, later identified as Vendikans, would enter into an interplanetary war sometime during the 18th century. The conditions of this war were stipulated in a treaty signed by both worlds. This was a simulated war with casualties determined by computer projections, and the people willingly killing themselves in disintegration stations. Legitimate targets in the war included vessels orbiting the planet. The reneging of this treaty by either side could result in a real war.
In 2267, the USS Enterprise visited the planet Eminiar VII. During the visit, when his ship and crew were threatened with destruction, Captain James T. Kirk ended the war abruptly by destroying the computers. Ambassador Robert Fox began work with the two planets to establish a lasting peace. (TOS: "A Taste of Armageddon")