Final answer:
Henry VIII's request for an annulment from Catherine of Aragon was denied by Pope Clement VII due to the risk of suggesting papal fallibility and the political influence of Catherine's nephew, Charles V. Henry responded by establishing the Church of England and marrying Anne Boleyn, triggering the English Reformation.
Step-by-step explanation:
In 1527, Henry VIII sought an annulment from his marriage to Catherine of Aragon, which is a declaration that the marriage was never valid according to Church law. Pope Clement VII refused the annulment primarily because doing so would undermine the papacy's authority and suggest that a previous pope, Julius, had erred in granting a special dispensation for their marriage.
Additionally, the political situation was sensitive since Catherine's nephew, Charles V of Spain, had control over Rome and reversing the decision could have weakened the already embattled Catholic Church amid the Protestant Reformation.
After the refusal, Henry VIII declared the Church of England independent of papal authority with the Act of Supremacy in 1534, and Archbishop Thomas Cranmer granted the annulment, paving the way for Henry to marry Anne Boleyn. This act is widely seen as the beginning of the English Reformation.