Answer:
King Henry VIII separated from the Catholic Church because under their policies, he wasn't allowed to divorce his current wife. England then becomes a mostly Protestant nation.
Explanation:
Although early signs of anticlericalism¹ had surfaced in England by the 1520s, Catholicism still enjoyed widespread popular support. As for Henry VIII, he "had no wish and no need to break with the church," as Andrew Pettegree puts it. No need because of the already substantial power King Henry had over the English church, and no wish because he was rater pious².
But by 1527, however, Henry had a pretty big — wait, scratch that — a HUGE problem. His first marriage, to Catherine of Aragon, had failed to produce a male heir. Henry also had infatuated³ with one of his wife's ladies-in-waiting⁴, Anne Boleyn, whose sister Mary had previously been his lover. Anne did encourage the king’s attention, but shrewdly⁵ refused to become his mistress, setting her sights on a higher goal.
So Henry asked Pope Clement VII to grant him a divorce from Catherine, arguing that the marriage was against God's will. That was due to the fact that she was briefly married to Arthur, Henry's late brother.
Under other circumstances, it wouldn’t have been that difficult for England’s king to get a papal dispensation⁶ to set aside his first wife and then marry another in order to produce a male heir. The reason why it was so difficult was timing. That SAME year — 1527 — the imperial troops of the Holy Roman Empire had sacked Rome itself, which forced Clement VII to take shelter in the Castel Sant'Angelo.⁷ At the time, the title of Holy Roman Emperor belonged to King Charles V of Spain — Catherine's beloved nephew.
With the papacy almost entirely under imperial sway, Clement VII was not inclined to grant Henry a divorce from the emperor’s aunt. However, he didn't want to fully deny either, so he had to stretch out negotiations, Cardinal Thomas Wolsey, over several years.
It was the clergyman Thomas Cranmer and the king’s influential adviser Thomas Cromwell — both Protestants — who built a convincing case that England’s king shouldn't be subject to the pope’s jurisdiction. Eager to marry Anne, Henry quickly appointed Cranmer as the Archbishop of Canterbury⁸, after which Cranmer quickly granted Henry’s divorce from Catherine. In June 1533, the heavily pregnant Anne Boleyn was crowned queen of England in a lavish⁹ ceremony.
Parliament's passage of the Act of Supremacy in 1534 solidified the break from the Catholic Church and made the king the supreme head of the Church of England.
Anne Boleyn, of course, would fail to produce the desired son (although she does give birth to Elizabeth I), and by 1536, Henry had fallen for another lady-in-waiting⁴, Jane Seymour. In October 1537, Seymour gives birth to Henry's first male heir, Edward VI, before dying of complications from childbirth only two weeks later. For the rest of Henry’s life, evangelical and conservative factions wrestled for influence—often ending with murderous results—but after Henry’s death in 1547, his son’s brief reign would be dominated by evangelical Protestant counselors, who were able to introduce a much more radical Reformation into England.
However, young Edward died in 1553, and his Catholic half-sister Mary I (or Bloody Mary) would reverse many of these changes during her 5-year reign. It would eventually be left to Elizabeth I, the daughter of Anne Boleyn who ruled England for nearly 50 years, to complete the Reformation her father begun.
¹anticlericalism - opposition to religious authority, typically in social or political matters.
²pious - devoutly religious
³infautuated - inspired with an intense but short-lived passion or admiration for
⁴lady-in-waiting - a female personal assistant at a court, attending on a royal woman or a high-ranking noblewoman
⁵shrewdly - in a way that shows sharp powers of judgement; astutely
⁶dispensation - exemption from a rule or usual requirement
⁷This is usually what the Mausoleum of Hadrian is called.
⁸Archbishop of Canterbury - the senior bishop and principal leader of the Church of England
⁹lavish - sumptuously rich, elaborate, or luxurious
