Tip: Inciting rebellion

I guess many people already know the technique/exploit to use monks/missionaries let a target province taken over by rebellion. Just in case you don't know yet...

There are a few distinctive advantages about it:

(1) The rebels could successfully take the province if it is poorly defended. Then it does not invade other places. Simple and predictable.
(2) A powerful foe could lose a lot of non-front line provinces in a short time, severely crippling it.
(3) This is a very effective way to take over an ally-controlled province without any diplomatic penalty.

Here are some additional tips:

(1) Only incite rebellion when there is little garrison. The rebels will attempt to attack the castle ONLY IF they think can win. If the garrison is too powerful, the rebels will wonder in the field amd does nothing (waiting to die by the winter cold, basically). So getting a rebellion in AI's well-defended front-line city helps very little, while you might end up dealing with it later. I read from multiple sources that the resulting rebels scale with the size of the defence. But I find the rebel's size does not go over a certain maximum - probably restricted by the agent's level?

(2) The chance of success tops at about 50% if your agent has the same religion as the target province. For example, if you use a six-star monk to incite rebellion from a Shindo-Buddhism province, the best chance you have is only a little more than 50%. However, if you use that monk to incite rebllion from an Ikko-Ikki or Christian province, the success rate could be a lot higher.

(3) Prepare your own army to beat the rebel-controlled province before the AI takes it back!

(4) Your agent has to have a reasonable success rate at this mission or the game would not allow you to even try. Fortunately, it is realtively quick and completely free to train monks (demoralizing armies on plain soldiers).

(5) The rebels do not take the city straight away even if it thinks it can win. Wait for an additional turn.

Ninja + Monk = Win

Teaming up Ninjas with a Monks will achieve some great effect. Use the Ninja's Sabotage army ability to prevent the super army from returning to defend a province, when the incited Rebel marches freely to take a ill-defended castle.