Coup (noun): Sudden change of government that is illegal and often violent. The rebels staged a coup and killed the sitting president.
Sedition (noun): The use of words or actions that are intended to encourage people to oppose the government. He was charged with sedition and sentenced to prison after the riot he incited killed five people.
Insurrection (against someone/something) (noun): A situation in which a large group of people try to take political control of their own country with violence. After the insurrection, there were many arrests and a great deal political turmoil.