King Philip II of Spain married Mary Tudor, the Queen of England, in 1554 with the aim of bringing England back to Catholicism. However, despite his efforts, he was not successful in his mission for a number of reasons.
Opposition from English Nobles: Many English nobles were opposed to the marriage, and feared that it would lead to a loss of English sovereignty to Spain. They also feared that Philip would try to impose Catholicism on the country, which was deeply unpopular with the majority of the English population.
Popular Resistance: Many ordinary English people were deeply committed to Protestantism, and were resistant to attempts to reintroduce Catholicism. This was especially true in the towns and cities, where Protestantism was strongest.
Mary's Death: Mary Tudor died in 1558, just four years after the marriage, and was succeeded by her half-sister Elizabeth I, who was a Protestant. Elizabeth reversed many of Mary's Catholic policies, and introduced a new Act of Supremacy which made her the head of the Church of England. This meant that even if Philip had succeeded in reintroducing Catholicism during Mary's reign, it would have been short-lived.
Political Instability: England was facing a period of political instability during the reign of Mary Tudor, with many Catholic and Protestant factions vying for power. This made it difficult for Philip to implement any lasting changes.
Overall, King Philip II's attempts to bring England back to Catholicism were thwarted by political, social, and religious factors that made it difficult for him to impose his will on the English people.