The year 948 has generally been assigned as that of the conversion of the Danes to Christianity; but, whatever the precise period may have been, the conversion was rather of a doubtful character as we hear of their burning churches, plundering shrines, and slaughtering ecclesiastics with apparently as little remorse as ever.  In the very year in which the Danes of Dublin are said to have been converted, they burned the belfry of Slane while filled with religious who had sought refuge there.  Meanwhile the Irish monarchies were daily weakened by divisions and domestic wars.  Connaught was divided between two or three independent princes, and Munster into two kingdoms.

The ancient division of the country into five provinces no longer held good; and the Ard-Righ, or chief monarch, was such only in name.  Even the great northern Hy-Nials, long the bravest and most united of the Irish clans, were now divided into two portions, the Cinel-Connaill and Cinel-Owen; the former of whom had been for some time excluded from the alternate accession of sovereignty, which was still maintained between the two great families of the race of Nial.  But, though this arrangement was persevered in with tolerable regularity, it tended little to the promotion of peace, as the northern princes were ever ready to take advantage of the weakness of the Meath men, who were their inferiors both in numbers and in valour.

The sovereignty of Munster had also been settled on the alternate principle, between the great tribe of Dalcassians, or north Munster race, and the Eoghanists, or southeners.  This plan of succession, as may be supposed, failed to work peaceably; and, in 942, Kennedy, the father of the famous Brian Boroimhe, contested the sovereignty with the Eoghanist prince, Callaghan Cashel, but yielded in a chivalrous spirit, not very common under such circumstances, and joined his former opponent in his contests with the Danes.  The author of the Wars of the Gaedhil with the Gall gives a glowing account of the genealogy of Brian and his eldest brother, Mathgamhain.  They are described as “two fierce, magnificent heroes, the two stout, able, valiant pillars,” who then governed the Dalcassian tribes; Mathgamhain (Mahoun) being the actual chieftain, Brian the heir apparent.  A guerilla war was carried on for some time in the woods of Thomond, in which no quarter was given on either side, and wherein it was “woe to either party to meet the other.”  Mahoun at last proposed a truce, but Brian refused to consent to this arrangement.  He continued the war until he found his army reduced to fifteen men.  Mahoun then sent for him.  An interview took place, which is described in the form of a poetic dialogue, between the two brothers.  Brian reproached Mahoun with cowardice; Mahoun reproached Brian with imprudence.  Brian hints broadly that Mahoun had interested motives in making this truce, and declares that neither Kennedy, their father, nor Lorcan, their grandfather, would