The invasion was legitimised by the provisions of the Papal Bull Laudabiliter , issued by Adrian IV in 1155 . The bull encouraged Henry to take control in Ireland in order to oversee the financial and administrative reorganisation of the Irish Church and its integration into the Roman Church system . Some restructuring had already begun at the ecclesiastical level following the Synod of Kells in 1152 . There have been significant controversy regarding the authenticity of Laudabiliter , and there is no general agreement as to whether the bull was genuine or a forgery .