The English Civil War was a series of conflicts fought between supporters of the English Monarchy, personified by Charles I of England and his son, Charles II, and the English Parliament, principally led by Oliver Cromwell, who disputed the absolute authority of the Monarchy over the country, and by extension, Parliament itself.
After two periods of conflict (1642-1646, 1648-1649), Charles I was executed in 1649, and England became a republican Commonwealth ruled by Cromwell. The King's son, Charles II, returned from exile in the Dutch Republic and gathered an army from Scotland, Wales, and Gloucestershire. Despite his military strength, the would-be King's army was defeated at the Battle of Worcester by Cromwell's much larger force, which routed the Royalists. Charles II escaped via St. Martin's Gate after the Earl of Cleveland led a diversionary cavalry charge.
Charles II evaded Parliamentarian scouts and eventually escaped to France by boat, where he lived out most of his exile in Breda. In the meantime, the remaining Monarchists began undermining Cromwell's control with the aid of one General George Monck, who kept Charles II abreast with information by letter.
Cromwell dissolved Parliament - an act previously committed by Charles I, which eventually led to the outbreak of war - in 1653, and was soon invited to be appointed Lord Protector of England, Scotland, and Ireland. By 1658, however, Cromwell was dead and his son had succeeded him.
In the ensuing chaos, Monck took control of London, and wrote to Charles II that Parliament would restore him to the throne if he granted amnesty to his father's enemies. This he did, and he returned to England, where he undid many of Cromwell's Puritan policies.