Reasons for the Royalist failure to defeat the Parliamentarians include shortage of ammunition, the relative lack of professionalism of their soldiers and the tactics of Essex, who compensated "for his much lamented paucity of cavalry by tactical ingenuity and firepower", countering Rupert's cavalry by driving them off with mass infantry formations. Although the numbers of casualties were relatively small (1,300 Royalists and 1,200 Parliamentarians), historians who have studied the battle consider it to be one of the most crucial of the First English Civil War, marking the high point of the Royalist advance and leading to the signing of the Solemn League and Covenant, which brought the Scottish Covenanters into the war on the side of Parliament and led to the eventual victory of the Parliamentarian cause.