Battlestar Galactica (1978)
In the original series, the Cylon war is also known as the Thousand Yahren War, the Thousand Year War and the Great Cylon Conflict.
The Cylon War began when the Twelve Colonies of Man came to the aid of an alien species called the Hasaris. This small and militarily-weak civilization was under attack by the Cylon army. The reasons for the Cylon-Hasaris war are never made clear; however, given the Hasaris' peace-loving nature, it is unlikely they were the aggressor. It is more likely that the Cylon picked them as a target. The Cylons were designed as war robots, and they needed a new enemy after they had destroyed their biological masters. Having never been commanded to cease fire, these warrior robots continued to wage war.
Despite the Colonies' help, the Hasaris civilization was eventually destroyed by the Cylons. Following their victory, the Cylons set their aim on destroying the Twelve Colonies, who had helped their enemies.
The war itself has never been discussed in detail. The few facts that are known are that the Colonial Battlestars were constructed shortly after the war had begun, that a large number of battles of all kinds took place, and that, at some point near the end of the war, Count Baltar was chosen to act as a liaison between both sides.
The Cylon War ended nearly a thousand yahrens after it had begun. The Cylons made an unexpected overture for peace through their agent, Count Baltar. The Colonials, weary of the war, accepted. However, the Cylons had no real intention to negotiate peace. Baltar had betrayed the Colonials, and the whole thing was a ruse to catch the Colonials off-guard. It worked almost perfectly, and in one sudden attack, the Twelve Colonies and all but two of the Battlestars (Galactica,Pegasus) were destroyed.
Following the destruction of the Twelve Colonies, the last Battlestar, Galactica, gathered the few survivors into a rag-tag fugitive fleet, and set a course for unexplored space, away from the Cylons. Their goal was to reach a mythical Thirteenth Colony, called Earth, in the hopes it had achieved a technological level high enough to protect them from Cylon tyranny.
Read more about this topic: Cylon War