* Political Instability: The death of King Edward VI in 1553 left England without a clear successor. Edward had attempted to exclude his half-sisters Mary and Elizabeth from the line of succession in favor of Lady Jane Grey, the granddaughter of Henry VII. However, this attempt was unpopular with many, including powerful nobles who supported Mary's claim.
* Catholic Support: Mary was a devout Catholic, unlike her father Henry VIII and brother Edward VI, who had pursued Protestant reforms in England. Her faith gained her the support of a large portion of the English population who favored a return to Catholicism.
* Military Support: Mary's supporters, led by the Duke of Northumberland, gathered an army and marched towards London to support her claim. Lady Jane Grey's forces were defeated without much resistance, and she was imprisoned.
* Recognition of Parliament: Mary's accession to the throne was officially recognized by Parliament, solidifying her position as the legitimate monarch of England.
Overall, Mary Tudor's rise to the throne can be attributed to a combination of political instability, religious affiliations, military support, and the recognition of her claim by Parliament.