Dublin enjoyed a sustained period of peace while Sigtrygg's men served in the armies of Brian. Sigtrygg never forgot the Ulaid's refusal of aid when he fled from Dublin, and in 1002 he had his revenge when his soldiers served in Brian's campaign against the Ulaid and ravaged their lands. His fleet raided Ulster, and he plundered Kilclief and Inis Cumhscraigh, taking many prisoners from both. They served under Brian against the Ulaid again in 1005, and against the Northern Uí Néill in 1006 and 1007. Cenél Conaill, the last of the Northern Uí Néill Kingdoms, submitted in 1011, and Brian was formally recognised as High King throughout Ireland.