Adama and Roslin surveying a Colonial battlefield
The Third Colonial Conflict (or Third Colonial War) occurred 60 years prior to the Cylon Holocaust and lasted for 10 years.
All that is known of the war is that Caprica and Sagittaron were on opposing sides. The Sagittarian fleet used warbirds and the Caprican Expeditionary Fleet used early Vipers, medivacs, flattops (Battlestar Galactica 0) and pre-Cylon War basestars and Raiders, the latter two were part of the Caprican Cylon Brigade (Battlestar Galactica 4).
This conflict may have been one of many wars fought between the Colonies prior to the Articles of Colonization. It was presumably the last conflict fought before the outbreak of the first Cylon War.