In spite of their conflict with the Scottish Royalists, the Covenanters then committed themselves to the cause of Charles II, signing the Treaty of Breda (1650) with him in the hope of securing an independent Presbyterian Scotland free of English Parliamentary interference. Charles landed in Scotland at Garmouth in Moray on June 23, 1650 and signed the 1638 Covenant and the 1643 Solemn League immediately after coming ashore.

The threat posed by King Charles II with his new Covenanter allies was considered to be the greatest facing the new English Republic so Oliver Cromwell left some of his lieutenants in Ireland to continue the suppression of the Irish Royalists and returned to England in May. He arrived in Scotland on July 22 1650, advancing along the east coast towards Edinburgh. By the end of August, his army was reduced by disease and running out of supplies, so he was forced to order a retreat towards his base at the port of Dunbar. A Scottish Covenanter army under the command of David Leslie had been shadowing his progress. Seeing some of Cromwell's sick troops being taken on board the waiting ships, Leslie made ready to attack what he believed was a weakened remnant (though some historians report that he was ordered to fight against his better judgment by the Covenanter General Assembly). Cromwell seized the opportunity, and the New Model Army inflicted a crushing defeat on the Scots at the subsequent Battle of Dunbar on September 3. Leslie's army, which had strong ideological ties to the radical Kirk Party, was destroyed, losing over 14,000 men killed, wounded and taken prisoner. Cromwell's army then took Edinburgh and by the end of the year his army had occupied much of southern Scotland.

This military disaster discredited the radical Covenanters known as the Kirk Party and caused the Covenanters and Scottish Royalists to bury their differences (at least temporarily) to try and repel the English parliamentarian invasion of Scotland. The Scottish Parliament passed the Act of Levy in December 1650, requiring every burgh and shire to raise a quota of soldiers. A new round of conscription was undertaken, both in the Highlands and the Lowlands, to form a truly national army named the Army of the Kingdom, that was put under the command of Charles II himself. Although this was actually the largest force put into the field by the Scots during the Wars, it was badly trained and its morale was low as many of its constituent Royalist and Covenanter parts had until recently been killing each other.

In July 1651, under the command of General John Lambert, part of Cromwell's force crossed the Firth of Forth into Fife and defeated the Scots at the Battle of Inverkeithing. The New Model Army advanced towards the royal base at Perth. In danger of being outflanked, Charles ordered his army south into England in a desperate last ditch attempt to evade Cromwell and spark a Royalist uprising there. Cromwell followed Charles into England leaving George Monck to finish the campaign in Scotland. Meanwhile, Monck took Stirling on the August 14 and Dundee on September 1, reportedly killing up to 2,000 of its 12,000 population and destroying every ship in the city's harbour, 60 in total.

The Scottish Army of the Kingdom marched towards the west of England because it was in that area that English Royalist sympathies were strongest. However, although some English Royalists joined the army, they came in far fewer numbers than Charles and his Scottish supporters had hoped. Cromwell finally engaged the new king at Worcester on September 3, 1651, and beat him — in the process all but wiping out his army, killing 3,000 and taking 10,000 more prisoners. Many of the Scottish prisoners taken by Cromwell were sold into indentured labour in the West Indies. This defeat marked the real end of the Scottish war effort. Charles escaped to the European continent and with his flight the Coventers hopes for political independence from the Commonwealth of England were dashed.

Battle of Worcester 1651

Aftermath

Charles II escaped after many adventures, including one famous incident where he hid from a Parliamentarian patrol in an oak tree in the grounds of Boscobel House. Charles was one of the few men in his army who regained a place of safety; about 3,000 were killed during the battle and a further 10,000 were taken prisoner at Worcester. Most of the rest were captured shortly afterwards as they fled. The Earl of Derby was executed, while the other English prisoners were conscripted into the New Model Army and sent to Ireland. Around 8,000 Scottish prisoners were deported to New England, Bermuda and the West Indies to work for landowners as indentured labourers. Parliamentary casualties numbered in the low hundreds.^[9]

After the battle, Cromwell returned to Aylesbury, Buckinghamshire; one of the parliamentarian strongholds and close to the seat of his late cousin; the civil war hero John Hampden. He stayed at the aptly named King's Head Inn, Aylesbury and it was here that he received the thanks of parliament for his final defeat of the royalists.

The Parliamentary militia were sent home within a week. Cromwell, who had ridiculed "such stuff" six months ago, knew them better now. "Your new raised forces," he wrote to the Rump Parliament, "did perform singular good service, for which they deserve a very high estimation and acknowledgement". Worcester was fought by a "nation in arms", by citizen soldiers who had their hearts in the struggle, and could be trusted not only to fight their hardest but to march their best. Only with such troops would a general dare to place a deep river between the two halves of his army or to send away detachments beforehand to reap the fruits of victory, in certain anticipation of winning the victory with the remainder. The sense of duty, which the raw militia possessed in so high a degree, ensured the arrival and the action of every column at the appointed time and place. The result was, in brief, one of those rare victories in which a pursuit is superfluous a "crowning mercy", as Cromwell called it.