Optimus Prime relates a history of the early war with all the excitement and eloquence of someone using a teleprompter for the first time. He tells how Cybertron once was at peace, but political corruption led to an energy crisis that split the Transformer race in two and began an unstoppable war. At this point, Megatron arose to take command of the Decepticons. Thankfully, the Autobots happened to stumble upon a lost ancient relic known only as the "Matrix", and it provided the Autobots with a new leader of their own: Optimus Prime. Searching for more energon, the Autobots took to space, and the Decepticons followed. They battled in space, and the Autobot ship crashed on modern-day Earth. Everybody survived and trans-scanned Earth vehicles with their eye-beams, and now their war continues... (tfwiki.net)