Some threads:
Absolute monarchy: how to not have a revolution every 10 years?

How do you make revolutions?

revolutions


Basically raise the taxes on your capital and remove them from your other provinces. If you have a Republic and want to go Monarchy, raise the middle class tax. If you have a Monarchy and want to go Republic, raise the lower class tax.

There is also the factor of having too many schools and such as well.