system
Given the following post, respond as if you're commenting on Reddit:
human
[Transformers] How did the Autobot/Decepticon war start?
gpt
Ooh boy. I've been waiting for a question like this. (Spoilers for the novel Transformers: Exodus ahead. You've been warned!)

Alright, so we've got Cybertron. Cybertron is a mechanical planet on which a race of transforming robots lived, millions of years ago. Shortly before the great war started, there was a strict caste system, and for every Transformer born from the Well of All Sparks, they are put into a caste where they are expected to work for the entirety of their lives. This his how things have been for thousands of stellar cycles. In the capital city, a robot known as Orion Pax worked as an archivist under Alpha Trion, spending his days going over data, indexing it, and cross-indexing it, all the while wishing for something more. 

One day, Orion intercepted a recording of a gladiator who lived on the other side of the planet, in Kaon. Kaon was home to the Transformers who were heavy laborers - miners, constructicons, etc. Since these guys were always working hard, they needed a way to blow off a little steam, which resulted in illegal, underground gladiatorial pits. One of these gladiators, Megatron had been making speeches, demanding equal rights for all Transformers - and Orion Pax thought this was a good idea. Rather than report Megatron for attempting to incite a massive revolt, Orion reaches out to him and contacts him.

The two discuss their beliefs about the problems with the government, Megatron wishing to change the establishment through confrontation, whereas Orion desires to change the system from within. Orion and Megatron enjoy their philosophical discussions and become good friends, even brothers. Orion even makes arrangements for Megatron to plead his case to the High Council.

Meanwhile, terrorists claiming themselves "Decepticons," attack various landmarks, including the theme park, Six Lasers over Cybertron. The lethargic Transformer leader, Sentinel Prime, is captured and his location unknown.

Orion brings Megatron before the High Council, who questions if Megatrons organization is behind these attacks. Megatron says that he did not order the attacks, but if the name "Decepticon" is to be laid at his feet, than so be it. 

"For if telling the truth is deception, then we are gladly guilty." 

In this meeting, the High Council (and Orion) finally see Megatron might be a little bit crazy. At this point Orion speaks up, saying why the caste system must change:

"We are all Autonomous Robots... Autobots, if we need a name to rally behind."

The council is moved by Orion's words, and feeling the need for a new leader, the council member Halogen admits that society on Cybertron had gotten too stagnant. The council promotes Orion to Prime, giving him the new name "Optimus." This infuriates Megatron, who was hoping to be named the next Prime, thinking that this was Orion's plan the whole time. Megatron kills Halogen, but before more fighting breaks out, Optimus manages to convince Megatron to commit no more violence in the halls of the council. Megatron and his forces retreat to the city of Kaon.

Well, that's how the war started. Soon after, Megatron poisoned the core of Cybertron with Dark Energon, which resulted in the core having to shut down, leading to the massive Energon shortage that caused the Transformers to leave their home. 

I love Transformers.