On 17 January 1649, the
Catholic Confederation signed a treaty with the
Duke of Ormond,
Royalist leader in
Ireland. Following the
Execution of Charles I on 30 January, they were joined by
Ulster Protestants who objected to his killing, and replacement of the monarchy by the
Commonwealth of England. However, their defection caused a split with Ulster Catholic
Eoghan Ó Néill, whose troops were some of the most effective in the Confederate army, and who now made a separate truce with
Michael Jones, Commonwealth governor of
Dublin. Seeking to secure Ireland as a base for the new king,
Charles II, Ormond
besieged Dublin in June, but was weakened by having to divert resources against Ó Néill. On 2 August, Jones defeated him at
Rathmines, a victory that allowed 12,000 mostly veteran
New Model Army troops under
Oliver Cromwell to land near Dublin unimpeded. At a Council of War held at
Drogheda on 27 August, Ormond and his commanders agreed to avoid open battle, but instead strongly hold key ports along the east coast. The garrisons were ordered to delay their opponents as long as possible, relying on hunger and disease to weaken them as winter approached. {{Location map many|Ireland|caption = Cromwell's 1649 campaign; key locations|relief=yes|border = black| width = 270| float = left This policy, while reasonable in itself, failed to take into account the large, modern, artillery train that accompanied Cromwell. These guns were too powerful for Drogheda's fortifications, which
was besieged on 3 September, and the walls quickly breached. When surrender negotiations broke down, the town was stormed on 11 September, and many of the garrison of 2,600 were killed. Despite being within the then-accepted rules of war, this act was unprecedented for the Wars of the Three Kingdoms, and Cromwell later admitted it was intended to deter future resistance. Cromwell returned to Dublin, while Ormond retreated to the Confederate capital,
Kilkenny. Sending a detachment against Ó Néill, who was negotiating a return to the Confederacy, Cromwell and his main force advanced on
Wexford. This port was an important base for Confederate
privateer attacks on English merchant ships, and provided a link with the exiled Royalist court in
France. His army moved far quicker than Ormond anticipated since their supplies and siege artillery were transported by a naval squadron under
Richard Deane. Ormond despatched 1,000 men under
David Synnot to garrison Wexford, with his field army based at
New Ross to protect its supply lines. Cromwell's force of around 6,000 arrived outside the town on 2 October; two days later, a detachment led by Jones surprised the Royalist garrison of nearby
Rosslare, giving Deane a secure harbour. ==Siege==