Why did King Henry VIII of England ask the Pope for an annulment or divorce from Catherine of Aragon?

Catherine didn't have a male heir for Henry and he had to insure that there was a male heir so the crown would stay within the Tutor family. His hold on the crown was tentative at best and there were others who had a better claim on the throne than he did. One reason the Catholic Church gave him such a hard time Catherine's uncle was pope and supported Catherine in her battle with Henry.