civil war 
noun
A war between citizens of the same country: they signed a peace accord ending the country’s 12-year civil war [mass noun]: the country is on the brink of civil war...
- We can tell that they've had civil war after civil war and that much of their population is unemployed.
- This rivalry had involved civil wars, peasant uprisings, and religious strife of every description.
- This acted as the trigger for a series of civil wars, as reactionaries and progressives battled both with the French and each other.