The establishment of garrisons beyond the Pale in Ireland during the late 1540s initiated a process of piecemeal conquest which antagonised displaced Gaelic lords, drove them to seek foreign intervention and created strategic threats to the British polity where none had hitherto existed. Throughout the period from the late 1540s to the mid-1560s, Gaelic dissidents became embroiled with the French, the Scots and disaffected elements in England in intrigue which involved varying degrees of collaboration and which aimed at undermining the Tudor régime. For the first time the Gaelic lords' projection of the Irish cause in quasi-religious terms impacted in a real sense on the consciousness of France's leading statesmen. The highpoint of this convergence of interests occurred in the winter of 1549–50 when Henri II came closest to staging an invasion of Ireland via Scotland.

This episode took place at a critical phase in relations between France and the three kingdoms of the British Isles that revolved around two highly contentious issues – the dispute between France and England concerning the latter's determined hold on its few French possessions, and their conflicting interests in Scotland. Henri II's ascension to the French throne in 1547 and the concomitant ascendancy of the Guises, their joint support for Marie de Guise in Scotland, the vulnerability of the minority régime in England, the disturbed state of the Gaelic polity and strained relations between France and England in the late 1540s and early 1550s all augured well for Irish prospects of securing French intervention.