The Scots sent an army under the command of the Duke of Hamilton into England to fight on behalf of the King in July, but it was heavily defeated at Preston by a force led by Oliver Cromwell.

[14][15] Before they would permit him to return from exile in the Dutch Republic to take up his crown, they demanded that he first sign both Covenants: recognising the authority of the Kirk in religious matters and that of parliament in civil affairs.

[21] Fairfax accepted the commission to lead the army north to defend against the possibility of a Scottish invasion but was unwilling to strike the first blow against his former allies, believing that England and Scotland were still bound by the Solemn League and Covenant.

[21] A parliamentary committee which included Cromwell, his close friend, attempted to dissuade him, pleading with him to change his mind, but Fairfax remained resolute and retired from public life.

[28] Operations were hampered by persistent bad weather and the adverse conditions and a shortage of food caused much sickness in the English army, substantially reducing its strength.

Cromwell was not able to draw Leslie out and the English retired for the night to Musselburgh; their rest was disturbed by a party of Scottish cavalry raiding their camp in the early hours.

Members of the Covenanter government, concerned that their Godly war would be corrupted by feelings of personal loyalty to the King, asked Charles II to leave.

The road was left littered with abandoned equipment[34] and the men arrived, according to one of their officers, Captain John Hodgson, as a "poor, shattered, hungry, discouraged army".

These relied on the glowing end of a length of slow match, thin cord soaked in saltpetre, igniting the weapon's priming powder when the trigger was pulled.

The usual tactic against infantry was for the musketeers to fire on their opponents and once it was thought that they had been sufficiently weakened or demoralised the stand of pikemen would advance, attempting to break through the enemy centre.

They would discharge their pistols at very short range and upon coming into contact attempt to use the sheer weight of their mounts and the mass of their formation to force back their opponents and burst through their ranks.

[59] Cromwell states that "as to sound men [...] about 7,500 foot and 3,500 horse",[57] while the modern historian Trevor Royle estimates that a little over 12,000 were fit for action;[60] Reid gives 12,080.

Royle, among others, has pointed out that the idea that Leslie was pressured into leaving the security of Doon Hill due to amateur advice from the Covenanter clerics is a myth.

The English army in turn advanced out of Dunbar and took up defensive positions along the steep north bank of the Brox Burn stream, which roughly paralleled the Doon Hill ridge.

The rough ground and the limited room to manoeuvre between the Brox Burn and the steep northern slope of Doon Hill hampered this and it was incomplete when halted by nightfall.

This position, in the front line of the army, was, says Reid, "a most extraordinary place" for the baggage train, only explicable by its nearness to the road which would have enabled it to move off promptly if the way could be opened.

[70] The alternative view is that Cromwell always planned an all-out assault and a decisive battle; Peter Reese is a proponent, although he states that "the odds against the English ... were awesome".

Their officers scattered across the countryside in search of sounder shelter, their cavalry went foraging and unsaddled most of their horses and Major General James Holborne ordered that the musketeers should extinguish their slow match except for two men per company.

George Monck, with a slightly smaller force than Pride, was south of the cavalry, in position to cross the Brox Burn upstream of the road ford at Brand's Mill.

The camp of a small force of dragoons under John Douglas was to the rear of the cavalry, but it is not clear to what extent these troops had been disposed forward as pickets on the night of the battle.

[82][83] At approximately 4:00 am on 3 September English cavalry advanced to clear the Scottish pickets from the three militarily practicable crossing points of the Brox Burn: Brand's Mill, the road ford and north of Broxmouth House.

Reid and Royle separately write that the Lord General's Regiment, led by William Packer, crossed the Brox Burn north of Broxmouth, either alongside or behind Pride's Brigade.

[100] Cromwell ordered his cavalry to the north west, where the infantry struggle was taking place and a unit charged Lawers' troops in their right flank and their formation collapsed.

[101] In contrast, Reese's account has the Lord General's Regiment, under Cromwell's personal control, following Pride's Brigade across the rear of the cavalry battle and deploying to its left (south).

[49] All accounts agree that approximately 5,000 Scottish prisoners were marched south and that 4,000–5,000 Scots survived to retreat towards Edinburgh; over half of them formed bodies of infantry and the balance cavalry or stragglers.

In September 2015 archaeologists announced that skeletons found in mass graves near Durham Cathedral were the remains of Scottish soldiers taken prisoner after the battle.

[107] Cromwell took pains to persuade the citizens that his war was not with them; he promised that their property would be respected and allowed them to come and go freely, hold markets and observe their usual religious services, although the latter was restricted as most of the clergy had removed to Stirling.

[120] These more radical elements issued the divisive Western Remonstrance, which castigated the government for its failure to properly purge the army and further widened the rifts amongst the Scots.

[118][122] During December Charles and the Scottish government started to draw together what remained of Leslie's forces, as well as the Engagers who had been purged from it and Highland chiefs who had been excluded by their refusal to sign the Covenant.

[124] This allowed the English army to threaten both Stirling and Perth, while Leslie's men, faced with impending total defeat, started to desert in great numbers.