 By Máel Sechnaill's time this alternating succession passed between Clann Cholmáin in the south and the Cenél nEógain in the north, so that he succeeded Domnall ua Néill in 980.This system had survived previous challenges by outsiders including the kings of Ulster, Munster and Leinster, and the Viking invasions.In 980, Olav Cuarán, King of Dublin, summoned auxiliaries from Norse-ruled Scottish Isles and from Mann and attacked Meath, but was defeated by Máel Sechnaill at Tara.