An interplanetary war was a war fought by neighboring planets within a solar system, or between neighboring systems within a quadrant.
The Eminiar-Vendikar War was an interplanetary war that broke out during the 18th century. As a result of the war lasting well into the 23rd century, from 2247 to 2267, thousands of lives had been lost in their quadrant, not including those of the crew of the USS Valiant, which was lost in 2217. It was the belief of Ambassador Robert Fox that those lives and more would have been saved if the Federation had a treaty port in the system. As the USS Enterprise approached Eminiar VII in 2267, it ignored, at the behest of Fox, a Code 710, which Captain James T. Kirk warned may involve the ship or the Federation in their interplanetary war. (TOS: "A Taste of Armageddon")
Following the discovery of the loss of all life in the Malurian system, Spock was unable to explain the cause, stating that "in the event of an interplanetary war, there would be considerable radioactive residue. Our instruments show only normal background radiation." (TOS: "The Changeling")
Threat of interplanetary war loomed over the admission of Coridanite into the Federation in 2268. The Orions were major players against said admission. (TOS: "Journey to Babel")
In 2377, the Kraylor and the Annari were involved in an interplanetary war. (VOY: "Nightingale")