Anne Boleyn was a young lady-in-waiting to the queen when Henry first noticed her. He was married to Catherine of Aragon at the time, and displeased with his lack of a male heir. The Boleyn family pushed Anne to exploit his attention. The rest is history.
Anne most likely would've been a mere mistress were it not for the legitimate heir factor and her own ambitions: She was determined to be queen. That, and Henry VIII actually fell in love with her. His divorce from Catherine slowly became more about marrying Anne than about having a son. In 1527, Henry started speaking quietly about getting rid of Catherine. In 1534, he granted himself the annulment, but he had actually married Anne the year before.
Anne was not well liked in Henry's court, especially after she became queen and she soon lost the king's love. She didn't give him a son in their first few years of marriage (although she did produce a daughter), and another young lady-in-waiting soon caught Henry's attention. He wanted to marry Jane Seymour. In his quest to marry Anne, and in satisfying her desire to be queen, Henry had already succeeded in making himself the sole decision maker in matters of marriage and divorce. There was nothing to stand in the way when he fell out of love with Anne.
Of course, he needed a good reason for the divorce so he wouldn't lose the support of the people (any more than he already had). Thomas Cromwell produced one: Anne had committed adultery with several men, including her brother. The charge was almost certainly false. There was no evidence to support it. But Cromwell was in charge of the court, and she was found guilty. Anne Boleyn was beheaded in 1536, two years after the king removed the pope's influence from England so their marriage would be legitimate. Her daughter became Queen Elizabeth I.
While Henry VIII held the throne, England went through changes that would eventually lead to the creation of modern sovereignty -- a nation not beholden to the church -- though Henry never intended it. He was a walking contradiction, a devoted Catholic who rejected the Pope and founded his own religion; a king of the people and an educated humanist who executed tens of thousands of subjects. In the end, Henry VIII produced one male heir, Prince Edward, his son by Jane Seymour. Edward took the throne when his father died; he was 10 years old. He died of illness five years later, passing the crown to Henry's daughter by Catherine of Aragon, Princess Mary. Queen Mary's primary objective became reinstating Catholicism in England. She failed in her quest, though she burned hundreds of people at the stake in the process. Elizabeth I succeed her older sister and reigned for 45 years.
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