Clement's policy was to keep the papacy independent by leaning first toward the emperor and then toward France, and it collapsed in a single day. On 6 May 1527 an unpaid imperial army, largely German infantry with a strong Lutheran element, stormed Rome. The Swiss Guard was destroyed almost to a man covering the pope's escape along the covered passage to the Castel Sant'Angelo, where he was besieged for months while the city was looted, its population killed or scattered and its churches stripped. He came out only after agreeing terms and paying, and Rome as a centre of the Renaissance did not recover.
The English question ran straight through that catastrophe. Henry VIII wanted his marriage to Catherine of Aragon declared void, and the strongest argument against him was that a previous pope had granted the dispensation that permitted it, which no successor could lightly declare invalid. The decisive fact, though, was political. Catherine was the aunt of the Emperor Charles V, and from 1527 Charles was the man whose army held Rome and whose goodwill the pope needed.
Clement delayed, appointed a legatine court in England, and then in 1529 revoked the case to Rome, which was the practical end of Henry's hopes of a lawful annulment. Cranmer pronounced the marriage void in England in 1533; Clement gave sentence for Catherine in March 1534 and Parliament passed the Act of Supremacy in the same year.
A pope who could not act because a besieging emperor was the queen's nephew is the immediate cause of the English break with Rome.