The Irish Approach
O'Neill and O'Donnell's forces attempt a night march to link up with the Spanish trapped inside Kinsale. However, a severe thunderstorm, lightning, and poor communication leave the three Irish columns hopelessly lost and fragmented in the darkness.
Arriving cold, tired, and sluggish after hours of marching, the vanguard loses the element of surprise as English scouts detect their movement.
Mountjoy's Response
Lord Mountjoy senses an opportunity. Instead of remaining trapped in his entrenchments, he makes a decisive tactical choice to strike early.
English cavalry are sent forward across the Millwater stream to engage O'Neill's disorganized vanguard before the Irish can form up properly on the boggy terrain.
The Rout
The English cavalry assault breaks the Irish lines. Panicking, the Irish horsemen retreat directly into their own pikemen, completely collapsing the formation.
The rest of the Irish army begins to flee, pursued for miles by the English cavalry. The Spanish inside Kinsale, unaware of the rapid defeat unfolding just over the hill, fail to launch a sortie to support them.
The Spanish Capitulation
With the Gaelic army shattered and no hope of relief, Don Juan del Águila realizes his position within the walled town of Kinsale is untenable.
He negotiates highly favorable terms of surrender with Lord Mountjoy. The Spanish forces are permitted to leave Ireland with their colors flying, keeping their weapons and dignity intact as they board ships back to Spain.
The Treaty of Mellifont
Red Hugh O'Donnell flees to Spain to beg for further assistance but dies shortly after, allegedly poisoned. Hugh O'Neill retreats to Ulster, fighting a bitter guerrilla war for another year.
Eventually, O'Neill is forced to submit to the English Crown at the Treaty of Mellifont, effectively ending the Nine Years' War and stripping the Gaelic lords of their independent sovereignty.
The Flight of the Earls
Faced with continuous English harassment and the erosion of their power, Hugh O'Neill, Rory O'Donnell, and their followers board a ship in Rathmullan, County Donegal.
They flee to the European continent, hoping to rally Catholic support. They would never return. This exodus marks the definitive end of the old Gaelic order in Ireland, clearing the way for the Plantation of Ulster.