 Some time during the 1010s , Brian Boru divorced Queen Gormflaith , and she began to engineer opposition to the High King . Around 1012 , relations between Brian and Leinster had become so strained that revolt broke out among the Leinstermen . Sigtrygg aligned himself with the forces of Máel Mórda , leader of the revolt , and the chiefs Ua Ruairc , Ua Néill , and others . Together , they defeated Brian 's ally Máel Sechnaill near the town of Swords , and Brian for the moment was unable to render assistance . 
