The Thousand-Yahren War is the primary conflict between the Cylon Empire and an intergalactic federation including the Twelve Colonies of Man.

This conflict began when the Colonies aided the Hasari in taking back "their nation" from the Cylons. The exact nature of the Hasari and their relationship to the Colonies remains unknown.

Battles of the War

The following were known events during this conflict, in chronological order:

Battle of Cosmora Archipelago: This is the earliest known confict, with Commander Kronus and the Fourth Fleet victorious against the Cylons .

Attack on Umbra: A Cylon attack on Caprica, presumably on Caprican agricultural resources, which leaves Starbuck and several hundred children orphaned.

Battle of Caprica: This occurred during Leda's lifetime.

Battle of Molecay: This is the last known major battle with the Cylons. The Fifth Fleet, lead by the "legendary Commander Cain", is destroyed here, save Cain's battlestar, Pegasus.

Battle of Cimtar: The final coup de grâce, resulting in the fall of the Twelve Colonies.

Effects of the War

Given the war's duration, it appears that efforts normally occuring during peacetime were curtailed. Apollo mentions to Zac that they would be able to resume deep space exploration should there be peace with the Cylons. The Rising Star's maitre d' states that the festivities during the departure from their home galaxy remind him of a "time before the war". This might suggest that there were lulls between major battles of reasonable length, or he might very well have been speaking of the time before the exodus from the Colonies.

In addition, the Colonials set up numerous colony worlds far outside their galaxy, which included the prison planet of Proteus and agricultural settlements such as Sectar. These planets became cut-off from the Twelve Colonies, resulting in a loss of technological advancement, even regression; Proteus, for instance, uses Sixth-millennium starfighters that predates the mainstay seventh millennium Colonial Viper, heavily suggesting that the war took its toll on the supply and transportation lines between the main colonies and their smaller intergalactic interests to the point where whole worlds and outposts were forgotten about.

Conclusion

The Thousand-Yahren War ends at the Battle of Cimtar. Lord Baltar, a Colonial double-agent for the Cylons, tricks President Adar into believing the Cylons wished to negotiate a truce. The peace conference is a ruse, allowing a force of one thousand Raiders to destroy four of the five battlestars, including Adar's Atlantia, while a basestar fleet (and additional Raiders) destroy the Twelve Colonies.

With Baltar's agent, Karibdis, neutralizing the Colonial defense systems on Caprica, the Cylons are able to attack the planet without planetary resistance. Strafing runs and pluton bombs are used to devastating effect by the Cylon assault forces.

The final attack takes several centares. Reports transmitted from Sagitaria indicate that it was "in flames", which is likely the same situation echoed throughout the Colonies.

As an end result, countless humans are killed and the Colonies are neutralized as a home for the Colonials.

From the ruins of the Colonies, surviving Colonials are gathered into a motley fleet of 220 civilian ships and are escorted to safety by the last surviving battlestar, Galactica.

The bulk of the Colonial military is lured into a trap by the promise of peace, only to find themselves and the Twelve Colonies of Man in a fatal trap .

After 1000 yahrens of war, the humans of the Twelve Colonies vie for peace with Lord Baltar acting as diplomat. The peace is to become official at Cimtar, a moon believed to be neutral territory. Instead of peace, the Cylons launch their largest onslaught ever against the Colonials. The Cylons use a two-pronged attack, striking at both the peace delegation (including the battlestars) as well as the Twelve Colonies.

Cylon fighter groups of Cylon Raiders (numbering a thousand total, along with support fuel tankers) hide near the Cimtar moon in wait for their chance at attacking the battlestar fleet. The basestars are left free for bombardment of the Colonies.

Commander Adama of battlestar Galactica receives reports that a Viper patrol has discovered the massive, hidden Cylon Raider fleet near Cimtar. Adama warns President Adar, President of the Colonies and commander of battlestar Atlantia of an imminent attack, but Lord Baltar sways Adar from ordering a defensive posture for the battlestar fleet.

Adama readies Galactica's defenses against orders. The battlestar is able to defend herself when the Cylons arrive, but the other battlestars, following President Adar's pacifist lead, are not so fortunate and can launch only a fraction of its fighters in time.

The Cylon fighters use a variety of tactics, including kamikaze methods to destroy the battlestar fleet. The Cylons destroy battlestars Atlantia (with President Adar aboard), Triton, Pacifica, and Acropolis.

Leaving her Viper pilots behind temporarily after getting reports of bombardment of the Colonies, Galactica heads towards Caprica in a vain effort to protect her homeworld.

During Galactica's flight to the Colonies, the battlestar received reports as the Cylons cleared the jamming to allow their own targeting and communication equipment to function. In one broadcast, 31 cities were "known to be under heavy attack" on an unknown colony while another report mentioned a second wave coming in.

Cylon basestars sneak by Colonial defenses, allowing an undefended attack on the Colonies. The home planets are bombed and the Cylons exterminate almost all of the human population of the Colonies. Caprica's destruction is assured through the efforts of Karibdis, one of Baltar's agents, who disables Caprica's defense systems and is held responsible for a million Caprican deaths (Murder on the Rising Star).

A handful of humans are tasked by Adama, now commanding the last known surviving battlestar, to flee the Colonies in whatever spaceworthy ships they can find to create a motley caravan that abandons Colonial space, initially for the nearby planet of Carillon where they obtain supplies for the long journey to Earth. Their exodus -- via the dangerous but poorly defended Nova of Madagon rather than the logical waypoint of Borallus -- takes the Cylons by surprise, who change their tactics to eliminate an now-elusive, moving target.

Lord Baltar is initially considered expendable by the Imperious Leader after the human's traitorous work and set up for public execution. However, the Leader's sucessor reconsiders Baltar's execution and provides him with the means to chase Galactica and her fleet to finish humanity once and for all.

The Battle of Gamoray is a Colonial offensive to secure fuel for the Fleet from the Cylon base on Gamoray.

The battle begins with a daring commando raid to disable the anti-assault batteries on Gamoray. Once the planetary defenses are defeated, Galactica and a small group of Vipers move in to secure the base on Gamoray and begin the refueling operation. Pegasus is sent away from Gamoray towards the three basestars in the area, theoretically to draw the attack forces away from the currently vulnerable fleet.

Just as Galactica begins to assault Gamoray, Baltar prepares to launch an assault against Galactica. Combined with the fighter squadron on Gamoray, Baltar has the firepower of four basestars worth of Cylon Raiders at his disposal and plans to press his advantage. When Baltar receives word that Galactica has left the fleet undefended, he orders his Raiders to take advantage of the opportunity and destroy the civilian fleet.

Lucifer informs Baltar that the Imperious Leader is on Gamoray, as part of a delegation to dedicate a new facility. Baltar quickly redirects his Raiders towards Gamoray, hoping to curry favor with the Cylon leader by rushing to his defense. On the way to Gamoray, Baltar's Raiders encounter Pegasus. Commander Cain combines his force of Vipers from both battlestars into a spearhead that cuts through the Raiders. Cain's ship sustains heavy damage before Baltar suspects that Pegasus is being used as a decoy, and orders his Raiders to ignore the battlestar and head directly for Gamoray.

Once Pegasus makes it past the Raider forces, Cain heads directly for the three basestars. The act confuses both Commander Adama (because it wasn't part of the plan) and Baltar (as one battlestar is no match for three basestars). Cain orders all wounded and non-essential personnel into shuttles, escorted by all the remaining Vipers onPegasus. The shuttles headed towards the fleet, while Pegasus rushes towards the basestars at full speed.

Baltar determines that Cain is coming after him, and orders all Raiders to return to defend him (before they reached Gamoray). Galactica is spared as a result and finishes the refueling operations. Starbuck and Apollo break off from the shuttle escort when they determine the Raider force will not intercept the shuttles in their course back to the basestars.

When it becomes apparent that Pegasus will reach him before the Raiders can return, Baltar orders his basestar to withdraw, allowing the other two basestars to defend him. Cain plots a course between the two basestars as Apollo and Starbuck quickly close from behind. The basestars are in such close proximity to each other that they cannot fire on the Vipers without hitting each other. The Vipers disable the flank missile launchers on the basestars. Pegasus reaches the point between the two basestars and fires all of her missiles at point-blank range.

The resulting explosion blinds Apollo and Starbuck. When they were able to see again, there is nothing left but debris. With the Raiders inbound, Apollo and Starbuck retreat back to the Fleet.