Hmm, well, were you here for Underworld?
Basically, the gates of hell themselves split open. Feena Mason died of natural causes. The CIS became the techno union, which collapsed, the Black suns were betrayed by the Sith which led to the rise of the Red Ravens, neither of whom are major now.
There are two Mandalorian factions. The united clans, and the Mandalorian Empire. Isley Verd leads the empire and claims the title of Mandalore, which not everyone agrees with, because why wouldn't that be contested?
The Primeval were a thing, then they fell to civil war, and stopped being a major faction. Fragments of their crazy cult are still wandering about the galaxy causing problems, including such wonderful people as Warok the Defiler and Boethiah the war-child.
The Mandalorian empire has recently made allies with a criminal organization know as the Black Tie syndicate, which includes former commanding personnel who fled the republic after a failed coup attempt. The Black ties have gone to war against the Republic.
Another group, known as the Black Empire, is also going to war against the Republic, and they seem to be a bunch of slaughter-happy psychos who feel the One Sith didn't let them kill enough babies, or something, I'm really not tuned into One Sith politics, although I think someone killed their NPC emperor a while back.
Everyone is welcome to tell me how much of this I got wrong, there's been a lot of stuff I was too busy dealing with this year to keep track of all this crazy poodoo. Also, I think there were stolen snacks somewhere along the line. Oh, and #clonelivesmatter #don'tforgetdave #alihadrixdidnothingwrong #vivumgenevieve #droidsdon'tmatter #givecoruscanttothedroids #lunacyreigns #Ionlymadeuphalfofthose