The causes of the Civil Wars were diverse and arguably included a complex web of conflicting political, religious, and financial motivations. They almost certainly happened when they did because of unrest in Scotland – which had started the ‘Bishops Wars’ of 1639 and 1640 – and the ugly Irish Rebellion of 1641. Yet a very good case can be made that the Great, or First, Civil War in England actually began over who controlled military forces and supplies. The shape of the opening campaigns was almost entirely dictated by the need to secure munitions of all descriptions – and not least artillery. Moreover the apparent hesitancy of both sides, and lack of boldness in their opening moves, can be explained as much in terms of the mechanics of war, as through politics. Since it was the seat of control of artillery and ordnance supplies, as well as the centre of government, London was unquestionably the most important place in the kingdom. The King's abandonment of London was probably his greatest mistake of the entire war – yet this was, to a large degree, forced by his opponents. Seizure of the Ordnance Office and the Tower would put Parliament in possession of both the biggest stock of guns, and the heart of the system of supply. Next in importance were the provincial stores of ordnance – the ports, notably Hull and Portsmouth, and the militia stores of the counties. The gradually unfolding process of capture and denial of these important strategic objectives, becoming increasingly violent with time, is in essence the history of the opening phase of war itself, up to the Edgehill campaign.

The argument that the ‘English’ war actually began over who was entitled to take charge of the machinery of war, and to make war, is very completely supported by the events of the winter of 1641 to 1642. As early as 7 December 1641 Sir Arthur Haselrig put forward a bill which would have put Parliament in control of the Militia. Though this ultimately failed to proceed beyond a second reading, it was soon succeeded by the famous Militia Ordinance which was introduced to the House of Commons in January 1642. This was the instrument by which Parliament would finally claim the power to raise troops a few months later. An abortive Royalist bill on the subject was thrown out in April.