Cylon War
From Battlestar Wiki, the free, open content Battlestar Galactica encyclopedia and episode guide
The Cylon War was the conflict that ended over forty years prior to the events of the Re-Imagined Mini-Series. It involved the early Cylons revolting against their role of servants to the Colonials; while the Cylons used Raiders and basestars, the Colonials developed the first battlestars, of which Galactica was one.
Given that the Articles of Colonisation were signed fifty-two years before the Mini-Series (Colonial Day), it is possible that the Cylon War was what precipitated the unification of the Twelve Colonies.
Veterans of the War include William Adama, Commander Dash and Colonel Saul Tigh.