He sent a detachment of 5,000 men north under Robert Venables to take eastern Ulster from the remnants of a Scottish Covenanter army that had landed there in 1642.They defeated the Scots at the Battle of Lisnagarvey (6 December 1649) and linked up with a Parliamentarian army composed of English settlers based around Derry in western Ulster, which was commanded by Charles Coote.
Oliver Cromwell, who landed in Ireland in 1649 to re-conquer the country on behalf of the English Parliament.
He left in 1650, having taken eastern and southern Ireland, passing his command to Henry Ireton.
On the other hand, his critics point out that he made little effort to restrain his troops or to punish them afterwards for their conduct.
Arguably, the sack of Wexford was somewhat counter-productive for the Parliamentarians.
The massacre of the garrison in Drogheda, including some after they had surrendered and some who had sheltered in a church, was received with horror in Ireland and is used today as an example of Cromwell's extreme cruelty.
Tom Reilly in Cromwell, an Honourable Enemy (Dingle 1999), argues that what happened at Drogheda was not unusually severe by the standards of 17th century siege warfare.After a week-long siege, Cromwell's forces breached the walls protecting the town.Aston refused Cromwell's request that he surrender.Jones, however, launched a surprise attack on the Royalists while they were deploying on 2 August, putting them to flight.Jones claimed to have killed around 4,000 Royalist or Confederate soldiers and taken 2,517 prisoners.To some degree they may have been effective in discouraging future resistance.