Final answer:
James I and Charles I both adhered to the belief in the divine right of kings, which states that a king is granted authority by God and not answerable to earthly powers like Parliament. This theory created conflicts with Parliament and influenced subsequent events such as the Glorious Revolution.
Step-by-step explanation:
The theory of monarchy that both King James I and Charles I held was the belief in the divine right of kings. This concept, detailed in James I's book The Trew Law of Free Monarchies, asserted that kings are divinely appointed and are not subject to earthly authority, including Parliament. This theory faced challenges during their reigns, contributing to significant conflicts with Parliament and shaping the political landscape of the era.
James I believed he would be independent of Parliament and that he would automatically receive a generous allowance to support the monarchy. His staunch belief in his own divine right led to a contentious relationship with Parliament. Similarly, Charles II and James II both struggled with their relationship with Parliament and the religious makeup of England, with James II's Catholic practices and attempts at centralizing power around the throne contributing to the Glorious Revolution of 1688.