So the Umbarans live on Umbara, a planet in a nebula that barely gets any sunlight and so exists in perpetual shadow. Early in the Clone war they where members of the Republic but after their senator was murdered in one of the intrigues of that war the Umbarans left the Republic and tentatively became Separatists because neither side really tolerated neutrality. There is a four episode arc on season four where one of the most bloody battles of the entire clone war is fought.
Very little about Umbaran Culture is shown but Umbara is shown to have native creatures so deadly that they give experienced, fully equipped for battle clone troopers a and their Jedi Generals. The technology Umbara brought to battle was also a match or better than anything the Republic or Separatists brought to bear.
After the War the Umbara Attempted to strike out for independence but the Empire Curb stomped their war torn planet and claimed Umbara’s apparently abundant natural supply of Doonium, a metal that is used to make starship hulls. A not insignificant percentage of the hull of the death star and many star destroyers was most likely mined by enslaved Umbaran’s forced at blaster point to strip mine their home planet.
Umbara has always been isolated and is used to going its own way because of the isolating effect of the nebula their planet resides in. Unlike most worlds there are bottlenecks to approach, also the perpetual darkness the Umbarans evolved to live in is off putting for other species. So I’m Imagining an Umbaran resistance that starts off not part of the larger galactic resistance.
So you have a people who live on a planet that looks like a blacklight prog rock album cover with native critters so deadly even a Mandalorian would tilt their helmet in a rare gesture of respect. Their planet is the proverbial village in the mountain pass that has one clear way in or out. And because they have something valuable and are isolated the Empires worst excesses can be let loose without the larger universe finding out.
