When civil war broke out in England in 1642 both the English Parliamentarians and Royalists petitioned the Scots Covenanters for their support. The Covenanters had the strongest army across all three kingdoms, they had defeated the Royalist forces of Charles I with remarkable ease in the Bishop Wars of 1639/40. The Covenanters may have been miserable bastards but they were also very successful - like Andy Murray. But for many in Scotland the extreme religious and political policies of the Covenanters went too far they wanted to join the war on the Royalist side of Charles I. The civil war had reached Scotland, and Scots had a choice to make; support ultra-Presbyterianism, or support the monarchy, it was 'Sophie's Choice' for Rangers supporters
https://mountebanktours.podbean.com/e/30-war-of-the-three-kingdoms/