Although Charles appointed him commander of the militia in Northern England, Rich sided with Parliament at the start of the First English Civil War in August 1642. Many on both sides expected a short, relatively bloodless conflict and were shocked by the casualties incurred at Edgehill in October 1642. In early 1643, Rich tried to persuade his cousin and Army commander Robert Devereux, 3rd Earl of Essex to force Parliament to make peace; when this failed, he defected to the Royalists at Oxford. Although present at Newbury in September, he was treated with indifference by Charles and returned to Westminster in November, reportedly because he opposed the "Cessation" negotiated by Royalists in Ireland with the Catholic Confederacy.