In March 1646 a cessation of hostilities was arranged between Ormonde and the Catholics; and O'Neill, furnished with supplies by the papal nuncio, Rinuccini, turned against the Scottish parliamentary army under General Monro, who had been operating with fluctuating success in Ireland since April 1642.
On the 5th of June 1646 O'Neill utterly routed Monro at Benburb, on the Blackwater; but, being summoned to the south by Rinuccini, he failed to take advantage of the victory, and suffered Monro to remain unmolested at Carrickfergus.
Isolated by the departure of the papal nuncio from Ireland in February 1649, he made overtures for alliance to Ormonde, and afterwards with success to Monck, who had superseded Monro in command of the parliamentarians in the north.
On the commander-in-chief pronouncing himself as emphatically opposed to such a step, Sir C. Monro was sent out from England to take his place.
Impressed by the unsatisfactory positions in which the Allied troops found themselves on the peninsula, by the impossibility of their making any progress at their existing strength, and by the risks that the army ran in remaining on such shores without any safe harbour to depend upon for base in stormy weather, Monro, after examining the situation on the spot in the closing days of Oct., declared unhesitatingly for a complete withdrawal.