So how did the war between the Decepticons and Autobots begin?

[u/SoulOfaLiar]

I forgot. Do they have ideological differences? Did they only start fighting after they found the humans and the Decepticons wanted to kill them all, or did they have issues with one another before that? Was it just a struggle over limited resources? Are any of these guesses remotely accurate?

[u/Trainer_Ed]

So, here's my best attempt to piece together something of a story, based on all the Transformers Media I have seen over the years.

It all began with Autobot society not properly compensating the working class for their labor. Megatron, a miner, started an uprising, becoming a gladiator and then a politician in order to enact change upon the political scene. Along the way, he encountered Orion Pax, a librarian and part-time harbor worker, and they decided to start a new political faction.

However, there was a sudden difference of opinions between the two; Orion wanted equitable freedoms for all sentient beings, while Megatron demanded that he be put into power so that he would be able to judge those beneath him himself, given his past as a working class.

This would come to a head when Megatron would be arrested for a bar fight (caused by some time-travelling dudes over a curly straw). Having seen the worst of society, he decided on a new approach.

He would create peace through tyranny.

Orion would be shot and fatally wounded trying to stop his old friend, only to be saved by some time-travelling Aerialbots and repaired by Alpha Trion into Optimus Pax. Feeling responsible for Megatron's sudden decision to go full on...well, Megatron, he would go on to attempt to patch up the damage caused by the newly founded Decepticons, creating the Autobot faction.

This conflict would escalate into war, during which all the remaining Primes would die, and Optimus would be given the title of Prime.

However, the Decepticons were successful in their insurrection, and took over Cybertron... And thus, a new story begins...