One other thing (if anyone has mentioned it already, blame my speed-reading ): faction re-emergences can also occur. Generally speaking any province a faction had owned before being wiped out is a potential site for a re-emergence if its loyalty drops below 120% (note 120 NOT 100 for re-emergences - so always allow a margin). This is worth remembering when you are trying to foment rebellion in a large enemy empire, as you may not get what you expected! It's one thing making a single stack of peasants crop up to give your enemy a hard time, but when instead there are 5 stacks of top-flight troops in a faction re-emergence, your plans to quickly snap up the province can be thwarted.

Another useful trick - depending on whether you're already at war with the faction you're trying to destabilise, and whether the opportunity presents itself - is to isolate the enemy king by sea blockade, as this gives a huge "communication" penalty to his empire (he can't reach it, so the loyalty plummets). Even if it's only for a single year, the damage can be severe. This is but one of many reasons not to send your own king on an all-expenses paid, self-catering holiday in Malta