[quote=@Senor Herp]
40k/Dune/Star Wars, mind. That leaves room for light space magic/pyskers, as well as for proper artificial planetoid-scale megaprojects, although those'd be either yet to have been made or been put out of commission. I would not put it past War of the Worlds Martians to try and replace the planet's dead, mined-out core and make some kind of crudely unsubtle fusion reactor, a contained artificial star, to power an entire mechanized undercontinent beneath the planet's crust. Like a tiny Dyson sphere. I would also not put it past them to fuck it up and, instead of producing a stable fusion reaction they could harvest more energy from than they needed to spend to contain it, cause the entire planet to go up like Alderaan by making a pure fusion weapon the size of a tiny moon, causing immense damage to Earth. That'd leave the Martians with only any exterior population to work with on the other dead rocks and the asteroid belt, though, so one would have to work out how they'd have garnered enough numbers after waking up or while still in-transit stasis to pose a credible threat. Automated cloning, maybe, tubescum kids that never knew home. What do you think, Willy? Any of this spitballing sound like it's on the mark?
[/quote]Time.
Martians traveled thousands of years and reached a yet uncharted territory. They began rebuilding their civilization and even expanding it further than they ever could. Then they eventually spotted the Empire and how grand it had become in comparison which gave the leader of the time a good dose of sodium. So they watched and spread their net to know more about their fattened up enemy. And then they noticed the collapse and knew it was time to strike.
Martians don't have the numbers to overwhelm the entire Empire but they plan to abuse its divided state and gradually take control of them. Through the course of the RP they'll create entire puppet governments with them secretly in control.

EDIT: As for mechanism, they rather went for the fission and via a controlled chain reaction they made an improvised molten salt reactor out of the core. Thing is that while the reaction was under control the stabilit of the core itself was not. This eventually led to a growing margin of error, destabilization of the planet and then runaway chain reaction converting the rest of the core into nuclear fuel which would reach critical levels within a month. The Martians fled and left behind an accidental nuclar bomb with the size of a moon which detonated soon. The Martians thought this would also destroy human civilizations but they warded off most of the danger by an experimental shield they were working on for a while.
That's my idea.

[quote=@Arawak]
Okay maybe the martians aren't a good idea.  They sound really cartoony which is totally out of place in a RP where everything's supposed to more 40K or Dune in terms of style.  That other space RP where I had a species of telekinetic balls would've been more fitting for them if it wasn't for Aaron being all philosophical.
[/quote]Yeah, as if 40k is in any way a serious or grounded setting. Not to mention what I said about Martians turning the planet's core into a reactor is far less BS than many of the technologies pesent in 40k.
Yeah, I'd fit in just fine.