TheBoost said:

Thinkin' about the original "Star Wars," there's no reason to assume that there ARE any aliens in the Empire or the Rebellion. For all we know it's the Human Empire, the government for human beings, one of many governments in the galaxy far far away, and not of any particular concern to aliens, who all have their own governments with their own problems.

I was going to argue this, but after racking my brain for a few minutes, I can't think of any threat to alien species at all. It wasn't until the Holiday Special that the idea of Wookiees being enslaved by the Empire was introduced. Maybe Splinter of the Mind's Eye elaborates the Empire and aliens ideas. It's been a few years, so I can't tell you exactly what happened down on Mimban. And really, that is more relying on the EU, which I never like to do.