I was watching a "movie" someone made of Homeworld on youtube. Someone in the comments explained a lore they read, that the Taiidan were using the Galactic Council against the Kushan. The Kushan attacked the Taiidan, and the Bentusi intervened, attacking the Kushan, effectively destroying the Kushan. The Taiidan took over their homeworld, and sent the Kushan into exile.

Is there such a lore I can read? And where can you find it? Is it cannon, or just fan fiction?

The manuals in the extra section of the downloads has the lore info.