That is one of the ways that the newspaper reports a rebellion or uprising:
Rebellion in Sevastopol
The garrison troops of Sevastopol have been overpowered in a violent uprising. The crowds proclaimed to return to Ukraine.
Rebellions are triggered by when morale in the province is low. Morale is particularly low after being captured, but can also be affected by the number of wars, food shortages, distance from capital, and neighbors.
The best way to learn about province morale is to click on the little "i" button next to the province morale bar. This will pop up a box that lists the province morale, percent chance of revolt, and other influences of the morale.
So in this example the morale of this recently captured province is 25%. I happen to have one infantry guy there still, with an army strength of 2.8 which makes the probability of an uprising 12%.
This is actually fairly dangerous, as it is likely that the province will revolt, and the new owner will get the infantry unit as well. So I plan to add more troops before day change.
If I remove that infantry the listing will change to army strength zero, and chance of uprising raises to 28%
So if you definitely want to prevent rebellions you need to keep a strong enough army in the province to bring that chance of uprising down to zero. With a newly captured province having a morale of 25% you need an army strength of 7.0 or larger typically. That army needs to be in the province center. Keep in mind that armored units lose strength when moved into cities.
The alternative is to allow provinces to revolt and keep an armored car behind your front line to run around and chase down the revolting provinces. I usually do this, and I only put a garrison force in important cities.
I thought at some point, when the morale was very low it would go in independance (as stated by my ally) and since it never happened to me, I thought it was something different than a rebellion.
