Well, you know how people can turn to dictators in times of crisis? Napoleon, Roman emperors, Adolf Hitler, ect.? Well, the Terminus Systems would be in an even shittier situation after the Reaper War.
People would have no way to support themselves, pirates and bandits would run amok, and the Council wouldn't do a thing as they'd be busy building their own worlds back up. Tired of the Council's centuries of putting them on the back-burner, people would begin to unite in the Terminus.
Taking advantage of the situation, a turian warlord named Teronus Nero would begin to take anyone who wanted peace and order and form the Terminus Empire.
The empire would be a bit more heterogeneous than most Right-Wing regimes, but it would very expansionist, very structured and very anti-Council. Teronus and his Imperial Army would begin snatching neutral and crime-ridden worlds and instilling his imperial government on them, daring the Council to stop him.
He's not necessarily evil. I'd compare him more to Napoleon than I would Hitler. He really does want peace and order, but with him as supreme leader crushing anyone who dares oppose his order.
Hm. So the geth and Reapers are destroyed, right? Would there be an opportunity for someone to build look-alikes to the geth? Like, just smart as fuck robots?
Oh, then that means I'd have a legit faction on my hands. Various beings that ally themselves with/are servile to the Geth remnants. I think they'd be super into peace though. Not hippies, mind you, but definitely more apt to try and talk things out first before whipping out the pewpew's.
Yawp. They'd definitely be political activists, economic moguls, etc, but working from the shadows because I'd assume the galaxy is very Anti-Geth still.
As long as the guy isn't waging an active war and doesn't get in their business, they'll either keep a respectful distance or try to get in good with him.
Oh no, Teronus is a student of history. People will very quickly turn on you if you massacre them for no reason. He has a system to integrate planets into his empire peacefully. He will show no mercy to criminals or rebels, but innocents are his future citizens and he treats them like so. He's not afraid to go to any lengths to protect his empire though, so brutal torture is on the table.