Great War

The Great War (グレートウォー, Gurēto Wō) was the first and most violent outburst of fighting which started on the planet Cybertron, where the Autobots wage their battles to destroy the evil forces of the Decepticons.

History
The Great War is known by some chroniclers of Cybertronian history as the Third Cybertronian War. It was during a time of peace known as the Golden Age of Cybertron that after eons of planning, plotting, and building up strength, Megatron re-organized the Decepticons and finally attacked, setting off global conflict of staggering proportions for the sole purpose of challenging the Autobots for control of Cybertron.

Decepticon tactics were well-orchestrated, and Autobot casualties continued to mount until Optimus Prime arose from the Autobot ranks to become a warrior of great firepower and leader of great skill. With his help, Autobots were able to hold their own against the Decepticons.

Synopsis
Shortly after the war was renewed on Earth in 200XX, Megatron would encode a message to Cybertron on the Voyager Golden Record (also known as the Golden Disk) just in case he lost. Over time, he was reformatted as Galvatron (after suffing damages during the Battle of Autobot City), and the monster Unicron got involved too.

The Great War was officially ended by the forming of the Pax Cybertronia with the Autobots the victors and the Decepticons placed under heavy restrictions. A period of uneasy peace followed with the Predacons biding their time in preparation for their chance to challenge the supremecy of the Maximals. A number of Decepticons were granted amnesty.