The First Civil War - As the civil war was fought to decide important issues, political, ecclesiastical and economic, men of all classes were found on either side. Indeed it was common for families to be divided by their support for one side or the other. Old family rivalries and feuds were also a factor. There were some who wanted nothing to do with either protagonist at all and to be left to get on with their lives.
The peers naturally mostly favoured the King although a number of prominent peers declared for Parliament. The gentry were split evenly between King and Parliament. The merchant class tended to be undecided in its support. Some trading centres supported the King and others favoured Parliament. This was decided principally by location and often due to personal and financial motives rather than political or religious conviction.
Geography played an important role in the question of support for the rival factions. The section of England east of a line from the Humber to Southampton strongly supported Parliament, while the north, the west and Wales were mainly for the King.
Holding London and nearly all the other ports, the Parliament could levy customs, duties and taxes and was financially stronger. Its hold on the ports was secure, as the navy declared for the Parliament.
Neither party had an effective army. The only legal forces, the militia, were poorly trained except in London and were not liable to serve outside their county of origin, except in case of foreign invasion. Both sides tried to enlisted volunteers and both had resort to conscription.
Cavalry still played a large part in battles, and in cavalry the King had an advantage, for the nobility and gentry had a long military tradition and could afford the upkeep of horses.
Many of the nobility and gentry on both sides had military experience having served abroad in one of the many European wars at that time
After the first battle at Edgehill and an unsuccessful attempt on London, the King established himself in Oxford, which became his headquarters for the rest of the war. His friends and allies were so successful that by the autumn of 1643 he controlled of 75% of the Kingdom.
After being defeated at the Battle of Adwalton Moor near Bradford Parliament requested the help of the Scots who had remained neutral, but who felt that their church could not be secure unless Presbyterianism prevailed in England. By the Solemn League and Covenant the Scots undertook to join the war against the King, while Parliament promised, or seemed to promise, that it would adopt the Presbyterian system.
The trial and execution of Archbishop Laud was a result of this alliance. Early in 1644 the Scots invaded England. The Parliamentarian army, with the help of the Scots, was victorious at the Battle of Marston Moor near York on the 2nd July 1644. This proved a turning point in the struggle and ended the King's power in the north.
Charles’s own successes in the south could not counterbalance this disaster, but drove the Parliament to create a modern and effective army. By the Self-denying Ordinance all members of either House were required to resign their commissions, and so removed several incapable Parliamentarian leaders from their commands. A new army was formed to fight for Parliament, the famous New Model Army, composed of men who undertook to serve until the end of the war and to go wherever they were required. Sir Thomas Fairfax was appointed Lord-General, with Philip Skippon Major-General of Foot (Infantry) and Oliver Cromwell officially appointed Lieutenant-General of Horse (Cavalry) in June 1645.
At Naseby on the 14th June 1645, Fairfax won a victory which drove the King out of the Midlands. He then conquered the south-west, and in the spring of 1646 returned to besiege Oxford. Charles fled from Oxford in disguise and took refuge with the Scottish Army with whom he thought he would receive more sympathetic treatment.