The latter involved Royalists, Gaelic Catholic leader Eoghan Ó Néill, and Presbyterian militia, known as the Laggan Army, supported by Scots Covenanters under Robert Munro.

The Covenanter government, who provided support for Scottish settlers in Ulster, considered Cromwell and other leaders of the new Commonwealth of England dangerous political and religious radicals.

As Scots, they objected to the execution of their king by the English; as Presbyterians, they viewed monarchy as divinely ordained, making regicide also sacrilegious, and they transferred their allegiance to his son, Charles II of England.

After capturing Drogheda on 11 September, his main force headed south towards Wexford; Colonel Robert Venables was sent north with three regiments, or around 2,500 men, to take control of Ulster.

[9] Ó Néill's death in November 1649 and Coote's defeat of a combined Royalist/Covenanter force at Lisnagarvey in December left the Catholic Ulster army as the only remaining opposition to the Commonwealth in the north.

[12] They lacked both arms and artillery but after Ormond promised to send these from Connacht, they marched north, intending to divide Coote's troops at Derry from those commanded by Venables at Carrickfergus in the east.

[13] To do this, MacMahon established a line of garrisons with its northern end at Ballycastle, then moved south, intending to cross the River Foyle just below Lifford and maintain contact with Ormond through Ballyshannon.

[15] However, the supplies promised by Ormond failed to arrive, leaving MacMahon short of provisions, while on 18 June Coote was joined by an additional 1,000 infantry under Colonel Roger Fenwick sent from Belfast.

As Coote fed in reinforcements, the Irish musketeers fell back on their main force, which had no room to manoeuvre and was now subjected to devastating volleys at close range.