The English Civil War (1641–1651) was a series of armed conflicts and political machinations between Parliamentarians and Royalists. The first (1642–46) and second (1648–49) civil wars pitted the supporters of King Charles I against the supporters of the Long Parliament, while the third war (1649–51) saw fighting between supporters of King Charles II and supporters of the Rump Parliament. The Civil War ended with the Parliamentary victory at the Battle of Worcester on 3 September 1651.
The Civil War led to the trial and execution of Charles I, the exile of his son, Charles II, and replacement of English monarchy with first, the Commonwealth of England (1649–53), and then with a Protectorate (1653–59), under Oliver Cromwell's personal rule. 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 this concept was legally established only with the Glorious Revolution later in the century.
During his stay in Grantville, Court Doctor William Harvey read about the English Civil War and hastily returned to England along with copies of materials about the war. He presented his information to King Charles, who then commanded the arrests and deaths of important historical figures who were to be his enemies during the war, including Oliver Cromwell. Many of these people were still minor politicians at best.
Despite the instability Charles has caused in the realm, the civil war may not happen in this timeline. King Charles was crippled in a staged accident and his health declined.