When Ulster's warriors are disabled by a recurring debility (the pangs), the teenage Cú Chulainn single-handedly stalls Medb's invading army by invoking an ancient right to single combat at fords, defeating a new challenger each day. The defense holds not through numbers but by binding a large force to a sequence of one-on-one duels dictated by custom.
Queen Medb launches the invasion of Ulster after a pillow-talk inventory of possessions with her husband reveals he owns one prize bull she cannot match, so she resolves to seize an equally great bull, the Donn Cúailnge, by force. A personal status rivalry between spouses escalates into a full provincial war.
The two contested bulls, the objects the entire war was fought to possess, fight each other to the death at the story's end, leaving the land strewn with the loser's remains. The coveted prize is consumed by the very conflict waged to own it, so the war yields no lasting gain for either side.