A tale of two kings
Well, we've got a house divided and our own little War of the Roses-esque conflict here. Ironically enough, the sons of the once-rebel Énna are the defenders this time around.
September 1122: Earl Flaithbertach of Kildare, heir to King Brian's son Énri, backs the Breifnean rebel branch. Lord Mayor Bran of Ormond, Countess Dubchoclaigh of Connacht, Earl Máel-Brigte of Desmond, and Duke Indrechtach of Ulster, the most powerful of Ireland's lords, join with him. Now facing overwhelming odds, King Máel-Sechlainn becomes a coward.
October 12, 1122: Despite facing greater numbers, the Munsterians win the first major engagement of the war at the Battle of Kilkenny. They lose almost 500 men doing so. The King hires the 2200 mercenaries of the Breton Company to bolster his forces.
The rebels may have numbers, but I have money. I have to pay a large sum up-front and a monthly stipend to keep the mercs in my employ, but it's the only way I can hold out against the vast armies of Ulster.
November 7, 1122: While the King's last loyal vassal, the Duke of Leinster, holds the line valiantly against constant attack on Kilkenny, Máel-Sechlainn's host captures Lord Mayor Bran of Ormond, one of the principle rebel leaders, on the battlefield.
December 1, 1122: The Munsterian stronghold of Dublin is captured by rebels. King Máel-Sechlainn hires a much larger company of Breton mercenaries.
I'm officially on track to empty my treasury to these sellswords who now make up a vast majority of my army, but with luck, I can end the war before I run out of gold to pay them.
February 19, 1123: The Munsterians capture Waterford, Ormond, and march to meet the main host of 3000 rebels.
March 22, 1123: Over 1500 rebels are slain at the Battle of Leighlin in a resounding Munsterian victory. Just over 300 king's men are lost. The Breifneans disparage it as a "bought victory."
April 25, 1123: 1000 more rebels fall at Gowran, to only 119 Munsterians.
August 1, 1123: The remainder of the rebel host is crushed outside Dublin, over 1000 slain to only 60 king's men.
August 18, 1123: As the siege to retake Dublin begins, the king dismisses over 2000 mercenaries he can no longer pay for.