Final answer:
The English Civil War took place from 1642 to 1649, ending with the execution of King Charles I and the establishment of the English Commonwealth under Oliver Cromwell.
Step-by-step explanation:
From 1642 to 1649, the English Civil War raged between the forces loyal to King Charles I and those supporting the Parliamentary side led by Oliver Cromwell. This conflict arose from escalating tensions between the monarchy and Parliament, resulting in a full-scale war that saw the Royalists ultimately defeated by Parliament's New Model Army. The culmination of this struggle was the execution of Charles I for treason in 1649, marking a significant moment in history as it was the first time a reigning monarch was tried and executed by a legislative body.
Following the king's execution, the monarchy was abolished, and England was declared a republic known as the English Commonwealth, initiating the period of the English interregnum. Oliver Cromwell took the helm of this republic, but after his death and several political transitions, the monarchy was restored in 1660 with Charles II becoming king.