Ankh-Morpork Civil War
There are several events in Ankh-Morpork labelled as The Civil War. One of the most notable is the civil war where the monarchy was replaced with the Patricianship due to the actions of "Stoneface" Vimes. This happened on Grune 4, 1688 UC, over 300 years before the present time in Ankh-Morpork. A spectacular if historically dubious recreation of this event was the subject of Century of the Fruitbat Studios' biggest (and last) moving picture production, Blown Away.
Patrician Lord Vetinari seems to have brought relative peace and quiet to the city, the last civil war being about 30 years before the present time and described in Night Watch. This Glorious Revolution led to the ascent of Mad Lord Snapcase at the cost of Lord Winder.