I've never seen the "United Clans" as such, but in one DA game, this happened to an opponent.

The Drengin, who had been constantly increasing their taxes as my allies slowly conquered their worlds, were hit by the "galactic disease" mega event - which cut their morale in half - and the next turn, seven of their planets broke away to form the Drengin Federation. Interestingly, they were good-aligned, and eventually wound up a member of my alliance, surviving until the end of the game, though they lost their original capital and another colony to Korath spore ships.

I'm pretty sure that the "rebel" civilization has a different name for each race. Who were you playing as?