The English Civil War (1642–1651) was a series of armed conflicts and political machinations between Parliamentarians ("Roundheads") and Royalists ("Cavaliers") over, principally, the manner of England's government. The first (1642–46) and second (1648–49) wars pitted the supporters of King Charles I against the supporters of the Long Parliament, while the third (1649–51) saw fighting between supporters of King Charles II and supporters of the Rump Parliament. The war ended with the Parliamentarian victory at the Battle of Worcester on 3 September 1651.

The overall outcome of the war was threefold: the trial and execution of Charles I (1649); the exile of his son, Charles II (1651); and the replacement of English monarchy with, at first, the Commonwealth of England (1649–53) and then the Protectorate under the personal rules of Oliver Cromwell (1653–58) and his son (1658–59). The monopoly of the Church of England on Christian worship in England ended with the victors' consolidating the established Protestant Ascendancy in Ireland. Constitutionally, the wars established the precedent that an English monarch cannot govern without Parliament's consent, although the idea of Parliament as the ruling power of England was legally established as part of the Glorious Revolution in 1688.