Charles' attempted imposition of an Anglican Prayer Book on the Scottish Kirk in 1637 sparked off major controversy and a riot in St. Giles Cathedral. Leading Scottish nobles and clergy gathered together to sign a National Covenant in February 1638 in which they promised to defend their church against Anglicanism and Episcopalianism.
Charles responded to the Covenant with fury, regarding the signatories as rebels who ought to be crushed. He gathered an army together in spring 1639, determined to teach the Scots a lesson. The Scots responded in kind, raising a Covenanter army under the command of David Leslie, a Thirty Years War veteran. The Three kingdoms were hurtling towards the abyss.
The First Bishops War ended without major violence but resulted in humiliation for Charles. His army had little stomach for the fight and he was forced to conclude the war by signing the Pacification of Berwick and agreeing to several Covenanter demands. Angry and vengeful, Charles turned to his trusted ally, the Earl of Strafford, for advice. Strafford advocated a properly funded military campaign against the Scots but this would require finance and the support of Parliament, and so, in spring 1640, Charles called a Parliament, the first in England for eleven years.
Following the riot at St Giles, the signing of the National Covenant in 1638 may be interpreted as a declaration of Scottish national identify and a determination to defend the Kirk against Laudianism. Although the Covenant proclaimed loyalty to the Crown, Charles interpreted it as an assault on his authority and determined to suppress the 'rebels'. His later troubles flowed from this decision.