The Dendredans are a race of humans from the Milky Way.
When Ares first conquered Dendred more than a century ago, it was already far more technologically advanced than the Earth, but had long since achieved world peace and all but abandoned weapons and war of any kind . This made the conquest of a relatively simple matter for the warlord, who ruled with brutality for decades. In Ma'chello's rebellion, the entire population was wiped out, killed instead deliver him.
Ares re-sowed it with slaves from their other facilities, and the planet has been slowly recovering since. In recent years, Ares left Dendred in charge of his sister Eris, which remains in the body in Ma'chellos former wife Sharna. Today is Dendred a world too large for its population. Its cities can hold many billions of people, but nearly 400,000 currently holds it. Eris respond by clustering the natives in some key areas, leaving the rest of the planet that is slowly reclaimed by nature. Entire continents sit untouched, save by occasional Jaffa patrol and many abandoned cities are waiting for someone to take them back. (RPG: "Friends and Foes: Stargate Season Two")
Ironically the very genocide designed to crush the uprising has allowed to survive it. With so much empty space to occupy part of Ma'chello supporters could be hiding from Ares and his forces. When new people arrived, they integrated with them, teaching forbidden arts as technology and relating stories about their missing leader. Through them, the rebellion of Dendred endured and still is fighting the Goa'uld. Although much smaller and weaker than in Ma'chellos day they remain a thorn in Eris' and can easily grow again should the right leader appears. If SGC does somehow contact with the rebellion together they could drive Eris and the Goa'uld from Dendred forever.