The Covenanter forces
The signing of the Solemn League and Covenant during the English Civil War brought about an alliance between the Covenanters and the English Parliamentarians against King Charles. Representatives of the Covenanters sat on the Committee for Both Kingdoms in London, which directed the allied war-effort, and observers from the Kirk attended the Westminster Assembly, at which reform of the Church of England was debated.
The Covenanter invasion of England began in January 1644. Parliamentarian expectations were high, but Royalist resistance led by the Marquis of Newcastle thwarted the Scottish advance through northern England until the decisive victory of allied Scottish and Parliamentarian armies at Marston Moor in July 1644. English confidence in the Covenanters was further damaged by the campaigns of Montrose in Scotland during 1644-5 when Covenanter regiments were withdrawn from England to deal with Montrose. Scottish political influence in London was adversely affected by the army's lacklustre performance and Covenanter ambitions to impose strict Presbyterianism in England in order to unite the churches of the two nations were frustrated.