Tarellian Civil War

From Memory Alpha, the free Star Trek reference.

The Tarellian Civil War was a historical event on the planet Tarella. Though the cause of the war was unknown, it was known that the war reached a stage where one of the continents manufactured biological weapons which were then launched against its rival continent. The weapons themselves proved effective in killing or diseasing many on this affected continent. Unfortunately, for the attacking continent, due to factors unknown, they themselves soon felt the weapons influence. The war ended when both continents were diseased with the extinction of the species imminent. (TNG: "Haven")