The first of the Stewart Kingdoms to collapse into civil war is Ireland, where, prompted in part by the anti-Catholic rhetoric of the Covenanters, Irish Catholics launch a rebellion in October.

In reaction to Charles I's and Thomas Wentworth's proposal to raise an army manned by Irish Catholics to put down the Covenanter movement in Scotland, the Parliament of Scotland had threatened to invade Ireland in order to achieve "the extirpation of Popery out of Ireland" (according to the interpretation of Richard Bellings, a leading Irish politician).

The fear this causes in Ireland once the rebellion has broken out unleashes a wave of massacres against English and Scottish Protestant settlers.

The planners of the rebellion are a small group of Irish landowners, mainly Gaelic Irish and from the heavily planted province of Ulster.

Hugh Og MacMahon and Conor Maguire are to seize Dublin Castle, while Phelim O’Neill and Rory O’Moore are to take Derry and other northern towns.

The plan, to be executed on October 23, 1641 (Roman Catholic Feast of St. Ignatius of Loyola), is to use surprise rather than military force to take their objectives, then, in expectation of support from the rest of the country, to issue their demands.

The plan for a fairly bloodless seizure of power is foiled, however, when the authorities in Dublin hear of the plot from an informer (a Protestant convert named Owen O’Connolly) and arrest Maguire and MacMahon.