you have to put what you find into context im surprised you havent found this by now
Another reason King Henry invaded Ireland was because Pope Adrian IV, the only Englishman to have occupied the papal throne, had issued a papal bull Laudabiliter (1155) authorising the English monarch to take possession of Ireland. Religious practices in Ireland and organisation had evolved divergently from those of areas of Europe influenced more directly by the Holy See, although many of these differences had been eliminated or greatly lessened by the time the bull was issued in 1155. Further, the former Irish church had never sent its dues ("tithes") to Rome. Henry's primary motivation for invading Ireland 1171 was to control Strongbow and other Norman lords. In the process he accepted the fealty of the Gaelic kings at Dublin in November 1171, and he summoned the Synod of Cashel in 1172, which brought the Irish Church into conformity with English and European norms.
The pope asserted the right to grant sovereignty over islands to different monarchs on the basis of a document, later proved to be a forgery, called the Donation of Constantine. Doubts were cast by eminent scholars on Laudabiliter itself in the 19th century, but its effect was confirmed by letters of Pope Alexander III and by the facts on the ground. The Papal power to grant also fell within the remit of Dictatus papae (1075–87). While Laudabiliter had referred to the "kingdom" of Ireland, the Papacy was ambiguous about describing it as a kingdom as early as 1185.