The Federation-Cardassian War was a conflict between the United Federation of Planets and the Cardassian Union. The period from 2355 until 2359 was considered to be the height of the conflict. (DS9 reference: Star Trek: Deep Space Nine Technical Manual) Although fighting ended in 2366 when a ceasefire was agreed between the two powers, the state of war wasn't formally ended until 2370 with the signing of the Federation-Cardassian Treaty of 2370. (Last Unicorn RPG module: Ship Recognition Manual, Volume 1: The Ships of Starfleet)