Cromwell landed in August 1649 and the reconquest was completed by 1653 after storms of Drogheda and Wexford in which garrisons and numbers of townspeople were killed, and a long attritional campaign against guerrilla resistance in which crops were burned and civilians moved or starved. The settlement that followed transferred most Catholic-owned land to soldiers and creditors and ordered Catholic proprietors to remove themselves and their households across the Shannon into Connacht and Clare by May 1654 on pain of death. Thousands of prisoners of war and others were shipped to the West Indies as indentured labour. Ireland's population fell steeply between 1641 and 1652; William Petty's contemporary estimate of 616,000 deaths, mostly from plague and famine, is the source of the often-repeated claim of a loss of a third or more, and modern historians such as Toby Barnard, John Cunningham and Micheal O Siochru accept a very large loss while treating Petty's arithmetic as unreliable. The scale, the intent and the appropriate label for these events remain among the most contested questions in Irish historiography.
The English Commonwealth reconquered Ireland, confiscated most Catholic-owned land, ordered Catholic landowners to move west of the Shannon, and transported thousands of Irish to the Caribbean colonies
William Petty's contemporary calculation gave 1,466,000 for 1641 and 850,000 for 1652; modern estimates put the 1641 population at 1.5-2.1 million, of whom the great majority were Catholic. Petty reckoned 616,000 deaths from war, famine and plague, a figure most historians consider too high but which still frames estimates of a 15-25 per cent population loss. Catholic-owned land fell from about 60 per cent of Ireland in 1641 to under 10 per cent after the settlement.
The upper bound is William Petty's estimate of 616,000 excess deaths between 1641 and 1652, made in the 1670s from his own imperfect surveys and widely reproduced since; the lower bound reflects modern scepticism about Petty's baseline and arithmetic while still accepting a very heavy loss. Most of the deaths on any estimate were from famine and epidemic disease, including bubonic plague in 1649-52, aggravated by the deliberate destruction of crops and the movement of populations, rather than from direct killing.
The killing of the garrisons and some civilians at Drogheda and Wexford, the burning of crops and destruction of settlements in the guerrilla phase, the transportation of prisoners and vagrants to Caribbean plantations, and the confiscation and eviction under the Acts of Settlement are documented in Cromwell's own dispatches, in the Commonwealth's statutes and in the transplanters' certificates and Down Survey records.
Ireland, Barbados