They burned Warrensgrove House, but new life has sprung up in its courtyard.
The War of Independence claimed around 1,400 lives, and it is estimated that several thousand more people, whose numbers have never been officially counted, died in the subsequent civil war.
But those turbulent years gave rise to another type of casualty as well - that of architectural and cultural heritage. Between 1919 and 1923, some 275 Big Houses were blown up or destroyed by fire - the vast majority of them during the Civil War.
The Big House, seat of the Protestant Ascendancy, had come to symbolise a despised regime, even though British imperial power had already been displaced by then.
Radical elements on the Republican anti-Treaty side in the civil war were bent on doing away with the old order, and vanquishing a former ruling class that was already in serious decline.
It wasn't just the houses that were destroyed - their libraries, art collections and papers were destroyed too, obliterating whole chunks of history. County Cork was the epicentre of this spate of arson. One of the many ascendancy houses destroyed in the Rebel County was Warrensgrove, near Crookstown, which was burnt out in 1921.
Local agitators might have felt they had good reason to attack Warrensgrove: it belonged at the time to Augustus Digby Warren, the seventh of the Warren baronets, a family which had a proud but, for the time, unlucky allegiance to the British military.
The fifth baronet, Augustus Riversdale Warren, was a British army major who fought in the Crimean War, before going on to help put down the Indian Mutiny of 1857.
The original Warren ancestral home, Warren's Court near Macroom, was also destroyed in 1921.
After the burning of Warrensgrove, the Big House was abandoned, and instead the substantial courtyard buildings were developed as a residence. From the front windows you can gaze out across the courtyard at the towering ruin of the past. You can even contemplate restoring it…
There was enough room in those courtyard buildings to develop another substantial country house, which stands at 4,820 sq ft. And there are still 80 acres of land with the property, which you approach by means of a one-kilometre avenue through woodland, passing streams and a waterfall, until you come upon the crumbling mansion still standing sentinel.
The 'new' house has been extensively renovated in recent years by its present owners, although there wasn't much they could have done to change the layout even if they'd wanted to.
For the most part, the house is one room deep - railway carriage-style - so the rooms are naturally dual-aspect, and it's quite a long trek from one end of the property to the other.
The main formal reception rooms are to the right of the entrance hall on the ground floor, where the main staircase is.
First, you reach a drawing room, about 16 ft by 23 ft, and from there you go straight on through to the dining room, which has its own door to the garden.
Off the dining room is a tack room which also has its own exit. To the left of the entrance hall is the kitchen, which is about the same size as the drawing room opposite.
On through the kitchen, there's a family room, and when you go past this you reach a little hallway with a second staircase.
Off this hallway, there's a guest toilet, a utility room, and a large office or games room which measures over 31ft by 14ft.
On the first floor, there's a self-contained apartment consisting of an open-plan, L-shaped living room, dining room and kitchen occupying the whole eastern corner of the house, with an adjoining bedroom and bathroom. Steps lead down from this apartment to a separate entrance on the ground floor. Apart from that, the first floor is all bedrooms, of which there are five, three of them en-suite.
The master bedroom is at the opposite corner to the apartment, and has an en-suite bathroom and dressing room.
Great efforts have been made to boost the energy efficiency of the house - with four-inch insulation, solar panels, double glazing, and underfloor heating - and the energy rating has been dragged up to a reasonably respectable D1. The courtyard buildings altogether form a U shape, with the house at the northern end, facing south. The U includes an abundance of other beautiful stone outbuildings, not all of them converted.
Among them are four coach houses, three stables, various storerooms, and the old steward's house, which hasn't been restored. The front courtyard features a lawn and flowerbeds, while out the back of the house is a walled garden with fruit trees and a vegetable plot.
Separately, there's a farmyard with hay barns and extra stables, and an all-weather arena behind it. Of the 80 acres of land, about 15 acres are woodland and 65 acres are farmland.
The nearest town is Crookstown just over three kilometres away, where there's a church, primary school, hotel and restaurant. Cork city can be reached in a little over half an hour by car. The Warrensgrove Estate is for sale with Dominic Daly in Cork, (021) 427 7399, with an asking price of €1.5m.