You can invent any rules you like Lucky, they simply don't matter.
Once Croatia and the other declared independence, Yugoslavia no longer existed except in the minds of those dreaming of a fascist Greater Serbia. No matter what immaterial, irrelevant and ineffectual wishful thinking you cling to makes a difference to the situation.
Serbia thought they could impose their fascist rule over these independent countries. Ask yourself, was it worth it?
Just like Russia thinking it can impose it's fascist rule over an independent country. Already shown it was not worth it.
Homegrown independence movements have nothing to do with a Russian invasion Lucky. Not the same.
