[sam h]

I don't know about the legal argument, but ever since the Treaty of Westphalia, nearly all nation-states have reserved for themselves, and exercized when necessary, the right to stop secessionist movements by violence.

Does that make it "justified"? Not necessarily. But the fact that it is technically legal or illegal doesn't make it "justified" either. Both are in the eye of the beholder. But using violence to stop secession is certainly par for the course in the history of nation-states.