Mary I had several main aims as queen: 1) Restore Catholicism in England after it had been replaced by Protestantism under Edward VI. 2) Deal with obstacles to Catholic restoration such as Protestant opposition, landowners who benefited from dissolved monasteries, and her lack of an heir. 3) She took steps like persecuting Protestant opponents, restoring papal authority, and enforcing Catholic doctrine, though this approach faced criticism for being too harsh. 4) By 1558, England had become largely Catholic again through Mary's efforts, though resistance remained and her death soon allowed Protestantism to resurge under Elizabeth I.