With a high stability level nothing bad will happen (high is 90-100%). The lower your stability, the unhappier your people and thus the more frequent and intense revolts will happen. It is safe to say that a high stability level is key to not losing the game. Mind the use of not losing instead of winning.

Now keeping stability isn't that hard actually. There are several ways too keep it high, these modifiers are shown in the diplomacy screen with any country. (Shown here, the red circle circles the modifiers)









The modifiers are as follows:
- Cash
The most simple and plain thing to keep stability high is to have enough cash. You can crank it up by having 9 black zero's and you can tear it down by having 9 red zero's.
- Political unity (yellow stripe)A faction that has a lof of political divideness has less stability. Make sure you use your internal propaganda to keep up the unity and disturb your enemies political unity by funding different groups. It doesn't matter what ideology you fund, as long as it isn't their ideology it counts towards the negative stability effect.
- Unemployed MPU's
Enough MPU causes positive effect.
- Ethnicy
- Religion
-Culture } Now it gets harder with every province you conquer:
Because you can't change these three (as far as I know). Every province has its own ethnicy, religion and culture. When those factors differ from your country's it adds up to the negative effect on your stability. You can compensate these three factors with the other factors (money is perfect for compensating) and keep your stability steady that way. If that doesn't work because you're expanding too fast or you can't compensate then there are other options. These options hang together with Annexing, Colonizing and Puppeting. When you annex a region that completely differs from your country's culture etc. you take the full hit. However when you colonize it, the hit won't be that big. And last, when you are in deep trouble and need to act fast use puppeting. Make the problem provinces a puppet and you still control them (sort of) but without the stability hit. Divide et impera. Divide your country before it divides itself into hostile countries.

Alternatively, you can put garrison in provinces and that should help as well. Those rebellious little brats will think twice of revolting that way.

As you can see I colonized some and have one puppet.

Thank you for reading all the way through! If you have any comments or questions put them down here. Rate if you like.
Have this awesome album as a 'thank you'.