Okay - so the Transformers. Much like the original cartoon, the Autobots and Decepticons have been at war for millions of years. However, in IDW continuity there was never a crash landing on Earth with the main cast stuck under a volcano for millions of years. There was simply a huge war. A war that went on for a very long time, and spread by proxy across many worlds in a desperate quest for resources in order to win. Such was the devastation that Cybertron itself was rendered largely inhospitable.
Eventually, one of those worlds targeted by the conflict was Earth, with both the Autobots and Decepticons arriving. There they discovered Ore-13, a type of Energon, essential for Cybertronian life (the Ore-13 on Earth had been created by Shockwave in a weird experiment shortly before he disappeared - both Shockwave and the Dinobots were buried on Earth following a battle for millenia).
The discovery of Ore-13 lead to an escalation in the conflict. A traitor in the Autobot ranks lead to a pretty grim time for them, and the Decepticons laid waste to chunks of the planet. However, in time the Autobots were able to fight back, and eventually incapacitated Megatron. Starscream, taking command, took the Decepticon forces and fled to a distant asteroid.
Around the same time the Transformers also faced a new threat - or at least a very old one. Nova Prime, one of Optimus' predecessors long thought lost on a voyage of discovery with some of his most powerful warriors (including Galvatron, Cyclonus and Scourge, who are separate characters in this continuity) attacked having being trapped in a dead universe which had essentially enslaved them. This was defeated.
Humanity rebuilt it's capitals, and for obvious reasons became non too keen on the transformers, but Prime and many other Autobots remained undercover, working in secret with the Earth's governments to track down a few Decepticon stragglers. Meanwhile Starscream blew his leadership - the Decepticons were rudderless and fell to petty infighting, becoming a shell of their former self. Eventually Shockwave and Soundwave, in desperation, rebuilt Megatron into a new, sexy body, and he returned. This included leaving Hot Rod for dead, with a huge hole in him filled only by the Matrix of Leadership...
While Nova Prime had been defeated, Galvatron, Cyclonus and Scourge survived. They built an army in an attempt to defeat an evil dead universe entity called D-Void, which was the enemy of all life, and headed for Cybertron. Upon hearing this and assuming bad intentions, the Autobots left Earth, heading to confront him. Megatron also surrendered to Prime and travelled with them.
Turns out distrusting Galvatron was a good idea, as he was being an idiot, and manipulated by D-Void rather than battling him. What he thought would stop D-Void - feeding an artifact into Cybertron's core, in fact would have brought it into our universe. Galvatron also managed to force all the remaining Decepticons and his army, possessed by D-Void's influence, to combine together into one gigantic scary robot. Megatron stayed to fight this giant beast while Prime and Rodimus went after Galvatron, but Prime was too late. Cyclonus realised they were being deceived and joined Prime. In desperation, Optimus sacrificed the Matrix of Leadership in order to block D-Void, but after the dust settled the core of Cybertron was gone, leaving behind just the empty Matrix. Megatron was nowhere to be found. The Decepticons, weakened after their giant robot combiner excursion, were easily rounded up by the remaining Autobots.
And so we get to RiD and MTMTE. The war is over. What happens next?