There are two ways that rebels can grow in your country, if another player has a spy in your country they can fund rebels once per turn (Funding rebels will result in drop of weapons). Alternatively, if your country has low stability rebels can grow naturally and foment insurrection. Having rebels in your country will result in a drop in growth, stability and approval.
You can arrest political opposition from the Domestic tab of policies which has a chance to remove rebels and increase stability, however moving your nation more authoritarian. Alternatively you can attack the rebels resulting in loss of soldiers but is more efficient and cost-effective.
There are five levels of rebel threat,from least to most:
- Scattered Terrorists
- Open Rebellion
- Civil War