I wouldn't expect clarity on this from Larian.
In Divinity 1, the Black Ring that appeared on screen consisted of 5 guys. Those 5 generals were destroyed along with the Demon of Lies. Yet 15-20 years later, there's a massive army of ground forces, including some on another planet. The 20-year time frame between the end of BD and the Divine's removal from the field was when the forces of light were powerful, I'm not sure how the Black Ring conscripted or recruited so many humans.
The story also suggests that Rivellon has mostly been at peace, which suggests that Damian hasn't been conquering and enslaving other countries.
The only clue about the lands the Black Ring still has under firm control is a couple of guys in the mining office mentioning the bases in Yuthul Gor, where orc slaves work on building Flying Fortresses.
