The Cheapest Trick in the Book!

[Executor]

I think unrest can go up to only 500.
And you need an army to kill and pillage a province, and if you have an army you can maybe defeat the enemy, and if you can defeat the enemy than no need to pillage your own lands.
But yes if you know there's apsolutly no chance of victory and want to do as much damage as possible cause it's a tricky game, cause you can go from 40 lands to just your capital, and again to owning 40 lands, and so on.