Stopping Rebellions

[Marquis de Said]

This has probably been discussed in another post, but I will chip in my own experiences.
Province loyalty depends on a few things such as:

1. Religion: the more people of the same religion as you, the more loyal the province. Use priests/alims to convert the population.
2. How long you've held the province. The longer the better.
3. Some provinces are a lot more rebellious than others. Livonia, Portugal, Scotland, Ireland, and to a certain extent Prussia and Lithuania are rebellions waiting to happen. E.g. in my last game as the Russians in high, expert, I had held Livonia for 50 years and it still rebelled with a 400-strong garrison, just because the governor got a -40% happiness vice. (It had BF but no church.)
A special case are provinces owned by the Papacy. If you bump off the Pope and hold his provinces, he will reappear in one or more of them no matter what you do.
4. As referred to above, the governor's vices and virtues, namely the ones that affect happiness. Also the governor's dread. Assign a 4+ dread governor and you will likely subdue any disloyalty in a province, provided it has a sufficient garrison. After conquering a province, I assign the general with the highest dread as governor, and only later swop him for a guy with high acumen.
5. Building a watch tower+border fort and a church in a province will increase loyalty significantly.
6. Your king's influence affects province loyalty as well. The more the better, obviously.
7. Contact with your king. If a province island has no line of ships connecting it to your other provinces, it will lose loyalty.
8. Enemy spies reduce your provinces' loyalty. Build border forts or post spies to counter them. You will most likely need at least a 2-star spy to catch enemy spies if a province has no border fort.
9. Tax rate. The higher the tax rate, the more discontent the population.

IMHO, the best way to keep a rebellious province in check is to place a spy of your own in there. Even a 1-star spy can work wonders.
I hope this helps.

Said

[Duke of Gloucester]

Before finishing each turn, press the shift button to check province loyalty. Green means o.k., yellow means small chance of rebellion, red means significant chance of rebellion.

If you have the Viking Invasion expansion pack, use the autotax function. If not , you will have to micromanage taxation. Aim to make sure that each province has a loyalty of 120%. This way any accidents (vices of governors, death of king etc.) won't reduce loyalty.

Control as many sea lanes as you can. This effectively means your king is nearer to each province.

Hope this helps.

[Ludens]

Certain buildings also improve loyalty. Churches and monastries obviously, but also the first town watch building. But the most useful building is the borderfort: it spies on your enemies, it catches enemy spies/assassins and it improves hapiness.

However, there is an imbuilt feature in the game that creates a large drop in loyalty when you have conquered 60% of the provinces (along with some other bad things like more vices for your govenors and a headstrong diplomatic AI that won't ally with you anymore).

[The Grand Inquisitor]

7. Contact with your king. If a province island has no line of ships connecting it to your other provinces, it will lose loyalty.
Said

And so never, ever, invade an island province with your king. When the port falls over, your king will be out of touch with everywhere and you can expect widespread problems.