If I recall, it was for far more than just wanting sovereignty. I recall hearing of atrocities similar (but not of the same scope) to this one before Russia came down hard on Chechnya. I just pinged someone else (MarMema) who might have more details.
If you learn more please ping me
The Chechnyans blew up apartment buildings in Moscow in the 90s, bombed rail cars, and of course, we have the theater seige.
Truth has a way of getting in the way of the liars and defenders of the indefensible.