Why did Pope Paul III excommunicate King Henry VIII of England?

Pope Paul III excommunicated King Henry VIII in 1538 primarily because the king had formally declared himself the supreme head of the Church of England, effectively severing England's ties with the Roman Catholic Church.12

While the conflict originated from Henry VIII’s desire to annul his marriage to Catherine of Aragon—a request previously denied by Pope Clement VII—the formal break with Rome was solidified by the Act of Supremacy in 1534. By the time Paul III ascended to the papacy in 1534, the schism was well underway. Paul III, who was committed to church reform and the Counter-Reformation, eventually issued the excommunication as a response to Henry’s continued defiance of papal authority and his establishment of an independent national church. An earlier attempt at excommunication under Clement VII had been suspended, but Paul III ultimately proceeded with the measure as part of his broader efforts to assert papal control and address the challenges facing the church.34512