So, I'm not a expert, but I have found out how to PROPERLY destroy revolts:
Basically, if you fight a revolt country when your in war with a neighbor, there won't be enough army in the said revolt country to actually destroy it. You must make peace with any neighbor countries your in war with, and once your in peace, if you have armies activated, you will see the army surround the revolt country. Once you attack, THEN the revolt country will eventually die, and thus you will not have to worry.
It's not a glitch, and it's not unfair as most people say, the revolt country (again) actually expands from the lack of a proper army to destroy it, since said army is fighting on a war happening somewhere else.
It's not the people's fault, of course, because they can easily miss that small detail, but since I noticed I thought sharing it would be good for further explanation.