The conflict began in 982, when Brian was campaigning against the kingdom of Osraige. With Munster undefended, Maél Sechnaill attacked the Dál gCáis, destroying the sacred tree of Adair, under which many of the chiefs of the Dál gCáis had been crowned, including Brian's father Cénnetig, his brother Mathgamain and Brian himself. In response, Brian led an army into Westmeath where he plundered the land. Brian's fleet did suffer a setback when a squadron of his fleet attacked Connacht, where they killed a prince of Connacht, Muirgius, who was among the defenders. In retaliation, the Connachtmen attacked the ships, massacring the crews.