Oliver Cromwell with Sir Thomas Fairfax in command and Cromwell as Lieutenant-General of cavalry and second-in-command. At the critical Battle of Naseby in June 1645, the New Model Army smashed the King's major army. Cromwell led his wing with great success at Naseby, again routing the Royalist cavalry. At the Battle of Langport on 10 July, Cromwell participated in the defeat of the last sizeable Royalist field army. Naseby and Langport effectively ended the King's hopes of victory, and the subsequent Parliamentarian campaigns involved taking the remaining fortified Royalist positions in the west of England. In October 1645, Cromwell besieged and took
Clan Leslie to death but he escaped and rejoined King Charles and continued to fight. Leslie's Scottish Covenanter force was defeated by the Scottish Parliamentarian forces who were at this point in time loyal to the Parliament of England and Oliver Cromwell at the Battle of Dunbar (1650). Leslie successfully commanded the Scottish Argyll Government Royalist forces at the Battle of Carbisdale (1650) where he was victorious against Scottish Royalist forces commanded by James Graham, 1st Marquess of Montrose. Leslie's Royalist Forces were defeated at the Battle of Worcester in 1651. Leslie, who was now commanding Royalist forces, had supported the plan