The Battle of Dunbar was fought between the English New Model Army, under Oliver Cromwell and a Scottish army commanded by David Leslie, on 3 September 1650 near Dunbar, Scotland. The battle resulted in a decisive victory for the English. It was the first major battle of the 1650 invasion of Scotland, which was triggered by Scotland's acceptance of Charles II as king of Britain after the beheading of his father, Charles I on 30 January 1649.

After Charles I's execution, the English Rump Parliament established a republican Commonwealth in England. When their erstwhile ally, Scotland, recognised Charles II as king of all of Britain on 1 May 1650 and began recruiting an army to support him, the English dispatched the New Model Army, under the command of Cromwell. The army crossed into Scotland on 22 July, with a force of over 16,000 men. The Scots withdrew to Edinburgh, stripping the land of provisions. Cromwell attempted to draw the Scots out into a set piece battle, but they resisted, and Cromwell was unable to break through their defensive line. At the end of August, with his army weakened through disease and lack of food, Cromwell withdrew to the port of Dunbar. The Scottish army followed and took up an unassailable position on Doon Hill, overlooking the town. On 2 September, the Scots advanced towards Dunbar and the English took up positions outside the town. The English army was greatly weakened by sickness and lack of food, while many of the Scots' most experienced men had been dismissed in religious purges.

Before dawn on 3 September the English launched a surprise attack on the Scots, who were poorly prepared. The fighting was restricted to the north-eastern flank with the main contingents of English and Scottish cavalry fighting inconclusively, as did the English and Scottish infantry. Due to the terrain Leslie was unable to reinforce the fighting, while Cromwell used his last reserve to outflank the Scots. The Scottish cavalry broke and routed; the Scottish infantry made a fighting retreat but suffered heavy casualties. Between 300 and 500 Scots were killed, approximately 1,000 wounded and at least 6,000 were taken prisoner from an army of 12,500 or fewer.

After the battle, the Scottish government took refuge in Stirling, where Leslie rallied what remained of his army. The English captured Edinburgh and the strategically important port of Leith. In the summer of 1651 the English crossed the Firth of Forth to land a force in Fife; they defeated the Scots at Inverkeithing and so threatened the northern Scottish strongholds. Leslie and Charles II marched south in an unsuccessful attempt to rally Royalist supporters in England. The Scottish government, left in an untenable situation, surrendered to Cromwell, who then followed the Scottish army south. At the Battle of Worcester, precisely one year after the Battle of Dunbar, Cromwell crushed the Scottish army, ending the war.

The Anglo-Scottish War (1650–1652), also known as the Third Civil War, was the final conflict in the Wars of the Three Kingdoms, a series of armed conflicts and political machinations between Parliamentarians and Royalists.

The English invasion of Scotland in 1650 was a pre-emptive military incursion by the English Commonwealth's New Model Army, intended to allay the risk of Charles II invading England with a Scottish army. The First and Second English Civil Wars, in which English Royalists, loyal to Charles I, fought Parliamentarians for control of the country, took place between 1642 and 1648. When the Royalists were defeated for the second time the English government, exasperated by Charles's duplicity during negotiations, had him executed on 30 January 1649. Charles I was also, separately, the king of Scotland, which was then an independent nation. The Scots fought in support of the Parliamentarians in the First Civil War, but sent an army in support of the king into England during the Second. The Parliament of Scotland, which had not been consulted before the execution, declared his son, Charles II, King of Britain.

In 1650 Scotland was rapidly raising an army. The leaders of the English Commonwealth government felt threatened and on 22 July the New Model Army under Oliver Cromwell invaded Scotland. The Scots, commanded by David Leslie, retreated to Edinburgh and refused battle. After a month of manoeuvring, Cromwell unexpectedly led the English army out of Dunbar in a night attack on 3 September and heavily defeated the Scots. The survivors abandoned Edinburgh and withdrew to the strategic bottleneck of Stirling. The English secured their hold over southern Scotland, but were unable to advance past Stirling. On 17 July 1651 the English crossed the Firth of Forth in specially constructed boats and defeated the Scots at the Battle of Inverkeithing on 20 July. This cut the Scottish army at Stirling off from its sources of supply and reinforcements.

Charles II, believing that the only alternative was surrender, invaded England in August. Cromwell pursued, few Englishmen rallied to the Royalist cause and the English raised a large army. Cromwell brought the badly outnumbered Scots to battle at Worcester on 3 September and completely defeated them, marking the end of the Wars of the Three Kingdoms. Charles was one of the few to escape. This demonstration that the English were willing to fight to defend the republic and capable of doing so effectively strengthened the position of the new English government. The defeated Scottish government was dissolved and the kingdom of Scotland was absorbed into the Commonwealth. Following much in-fighting Cromwell ruled as Lord Protector. After his death, further in-fighting resulted in Charles being crowned King of England on 23 April 1661, twelve years after being crowned by the Scots. This completed the Stuart Restoration.