The English Civil War broke out in 1642, less than 40 years after the death of Queen Elizabeth I. Elizabeth had been succeeded by her first cousin twice-removed, King James VI of Scotland, as James I of England, creating the first personal union of the Scottish and English kingdoms.As King of Scots, James had become accustomed to Scotland's weak parliamentary tradition since assuming control of the Scottish government in 1583, so that upon assuming power south of the border, the new King of England was affronted by the constraints the English Parliament attempted to place on him in exchange for money. Consequently, James's personal extravagance, which resulted in his being perennially short of money, meant that he had to resort to extra-parliamentary sources of income. Moreover, increasing inflation during this period meant that even though Parliament was granting the King the same nominal value of subsidy, the income was actually worth less.

This extravagance was tempered by James's peaceful disposition, so that by the succession of his son Charles I in 1625 the two kingdoms had both experienced relative peace, internally and in their relations with each other. Charles followed his father's dream in hoping to unite the kingdoms of England, Scotland and Ireland into a single kingdom. Many English Parliamentarians were suspicious of such a move, fearing that such a new kingdom might destroy old English traditions that had bound the English monarchy. As Charles shared his father's position on the power of the crown (James had described kings as "little gods on Earth", chosen by God to rule in accordance with the doctrine of the "Divine Right of Kings"), the suspicions of the Parliamentarians had some justification.