The English Civil War was a series of conflicts between 1642 and 1651, primarily between the supporters of King Charles I and those of the Parliament. The war arose from disputes over how England should be governed and issues of religious freedom. The conflict led to significant battles, including the Battle of Naseby, and resulted in the trial and execution of Charles I in 1649. Following the war, England was declared a republic under the leadership of Oliver Cromwell, marking a significant shift in the country's political landscape.