The war between the two peoples of the planet Cheron, distinguished only by which side of the body was black and which white, which ended in the death of everyone on the planet.
Cheron lay in an uncharted southern part of the galaxy. Its people were black on one side and white on the other, and those black on the right had long held those black on the left in subjection.
In the Original Series episode Let That Be Your Last Battlefield, the Enterprise, on an urgent mission to decontaminate the planet Ariannus, picks up the fugitive Lokai in a stolen shuttle and then Commissioner Bele, who has pursued him for fifty thousand years. Bele takes control of the ship by force of will and steers it to Cheron.
Sensors find the cities intact and the population gone, the whole race having destroyed itself. Unable to give up their hatred, the two beam down to continue the chase among the ruins.