And there you have it. 100 years of alternate history. We've seen House ua Brian rise from a modest noble family in southern Ireland to a great and renowned dynasty holding claim to two kingdoms. 1166 marked the lineage at its most resplendent.
The ua Brians would go on to face continuing adversity in the coming years, as Duke Gudbrand declared war to reclaim England, swindling Norfolk to back his cause and calling on the aid of the distant Spanish realm of Navarra. King Murchad would be badly wounded in personal combat with the pretender, though he made a full recovery from the injuries in later life. The conflict ended with the assassination of Duke Gudbrand by the Earl of Essex, who swore fealty to King Brian and marked the largest expanse his borders would ever cover. King Murchad lost no battles over the entire course of the war, despite being outnumbered in several.
King Murchad finally left the world on June 7, 1173, after a period of infirmity at age 48. His son, King Brian II, became the youngest ever King of Ireland and England at 21, ruling alongside the Ulsterian Queen Cristina. The ambitious young liege would go on to wage war on Duke Stigand of Norfolk, former supporter of the traitorous Gudbrand, to unite southern Britain under the Irish-English crown. The momentum of the war was on King Brian's side, despite a brief Connachtian rebellion led by the heirs of House ua Brian of Breifne lasting from 1174 to 1176.
This momentum would finally be halted in August of 1176 when Duke Trond of Gloucester, son of Duke Gudbrand, declared himself King of England and called in the the aid of Norfolk (already at war with King Brian) and Somerset, once loyal to the crown. The royal host found themselves outnumbered three to one due to the stubborn insistence of Queen Cristina to use most of the Ulster levies to press her own ducal claims on Ireland's lesser lords.
Though they fought valiantly, King Brian's loyal men were dealt a decisive defeat at the Battle of Bath on December 4, 1176. This marked the effective end of Ireland's claim on mainland Britain, and the Kingdom of England would pass back to the Saxons. Nonetheless, Ireland would only grow stronger and more independent, becoming an unassailable fixture of northern Europe under ua Brian monarchs for generations to come, while the petty kingdoms of Britain continued to squabble and claw for territory.
Thus ends our tale...