British historian John Morrill wrote that the Act and associated forced movements represented "perhaps the greatest exercise in ethnic cleansing in early modern Europe.

"[1] The Act was passed on 12 August 1652 by the Rump Parliament of England, which had taken power after the Second English Civil War and had agreed to the Cromwellian conquest of Ireland.

Ten named leaders of the Royalist forces in Ireland, together with anyone who had participated in the Irish Rebellion's early stages and who had killed an Englishman other than in battle, lost their lives and estates.

The first ten people on this list are: The list does not recognise many of the titles created by Charles I and Charles II, such as James Butler's Marquessate of Ormond, created on 30 August 1633 The Act made a distinction between the rebels of 1641 – who were deemed unlawful combatants – as against those who had fought in the regular armies of Confederate Ireland, who were treated as legitimate combatants provided that they had surrendered before the end of 1652.

[4] The remaining leaders of the Irish army lost the vast majority of their estates, causing Catholic land ownership to fall to just 8% across the island.

[5] To have been merely a bystander was itself a crime, and anyone who had resided in Ireland any time from 1 October 1649, to 1 March 1650 and had not "manifested their constant good affection to the interest of the Commonwealth of England" lost three-quarters of their land.

[10][11][12][13] Some Irish prisoners were forcibly sent on ships to the West Indies where they became indentured servants on sugar cane plantations belonging to British colonialists.

[citation needed] The vast majority of the population, outside the 6 counties that would later be partitioned into Northern Ireland, were expected to remain where they lived, and to continue as tenant farmers or servants under the new freeholders.