However, this was offset first by defeat at Lostwithiel in September, then lack of decisiveness at the Second Battle of Newbury in October. The review coincided with increasing dissatisfaction as to the conduct of certain senior commanders in July 1644, a Parliamentarian force under Sir Thomas Fairfax and Oliver Cromwell secured control of Northern England by victory at Marston Moor. On 17 February 1645, the New Model Army Ordinance became law, with Fairfax being appointed Captain General, or commander in chief, and Philip Skippon being appointed Major General of the Foot.
In response, the Committee of Both Kingdoms conducted a wide-ranging review of further military needs and recommended the establishment of a centralised, professional force.
On 19 November 1644, the Parliamentarian Eastern Association announced that they could no longer meet the cost of maintaining their forces, which then comprised about half the field force available to Parliament. The weakness of this system was the reluctance of locally-raised troops to serve outside their "home" areas, a problem for both sides during the war. When the First English Civil War began in August 1642, many of the largest militia were based in Parliamentarian areas like London, while Royalist counties like Shropshire or Glamorgan had fewer than 500 men. The muster roll of February 1638 shows wide variations in size, equipment and training the largest and best trained were based in London with 8,000, later increased to 20,000. Founded in 1572, these were organised by county, controlled by Lord-lieutenants appointed by the king, and constituted the only permanent military force in the country. The forces raised in 1642 by both Royalists and Parliamentarians were based on part-time militia known as Trained bands. Sir Thomas Fairfax, appointed commander of the New Model in April 1645 Ultimately, the Army's generals (particularly Oliver Cromwell) could rely on both the Army's internal discipline and its religious zeal and innate support for the " Good Old Cause" to maintain an essentially dictatorial rule. Although the Army's senior officers did not share many of their soldiers' political opinions, their independence from Parliament led to the Army's willingness to contribute to the overthrow of both the Crown and Parliament's authority, and to establish a Commonwealth of England from 1649 to 1660, which included a period of direct military rule. Many of its common soldiers therefore held dissenting or radical views unique among English armies. The New Model Army was raised partly from among veteran soldiers who already had deeply held Puritan religious beliefs, and partly from conscripts who brought with them many commonly held beliefs about religion or society. This was to encourage their separation from the political or religious factions among the Parliamentarians. To establish a professional officer corps, the army's leaders were prohibited from having seats in either the House of Lords or House of Commons. It differed from other armies employed in the 1638 to 1651 Wars of the Three Kingdoms in that members were liable for service anywhere in the country, rather than being limited to a single area or garrison.
The New Model Army was a standing army formed in 1645 by the Parliamentarians during the First English Civil War, then disbanded after the Stuart Restoration in 1660.