The Civil War started on 22 August 1642 when Charles I raised his standard at Nottingham. He soon moved on to establish his headquarters at Oxford from where he controlled the west.
The Parliament at Westminster controlled the south and east. From there it raised troops and imposed two new forms of taxation, the assessment and the excise (a tax on the purchase of goods). These yielded far greater sums than any previous parliamentary taxation, and were, ironically, as burdensome as any of Charles I's taxes.
Presbyterians and Independents
Divisions developed within Parliament between the Presbyterians who wanted to end the war quickly and were willing to negotiate with Charles I, and the Independents who wanted a vigorous prosecution of the war to force their terms on a defeated King.
These names originally derived from disagreements about how the Church should be organised - the Presbyterians wishing to see a church ruled by 'elders' enforcing strict doctrine and the Independents arguing for toleration towards non-conformist congregations. This reveals how religion lay behind many of the divisions in the Civil War.
The Self-Denying Ordinance
In 1644-5 Independent military leaders, particularly the MP Oliver Cromwell, accused the Parliamentarian generals, the Earls of Essex and Manchester, both of them Presbyterian Members of the House of Lords, of not fighting the war forcefully enough.
In February 1645 the Independents pushed an Ordinance for the reorganisation of the Parliamentarian army through Parliament. Then in April 1645 the Houses passed the Self-Denying Ordinance, which forced Members to choose between continuing to sit in Parliament or retaining their commissions in the Army - although Cromwell managed to continue in both.
New Model Army
This New Model Army won a succession of victories, ending with the surrender of Charles I and of Oxford in June 1646.
The war was in some ways the easy part, for now that Charles I had surrendered some sort of agreement had to be made with him. Parliament embarked on these negotiations divided between Presbyterians and Independents and with a new political force, the New Model Army, beginning to make its power felt.