In 1558, Queen Mary I of England (eldest daughter of Henry VIII) died. Mary Tudor had ruled England since 1553 and had been a devout Catholic and had persecuted Protestants during her reign.
About 300 Protestants who would not accept Catholic beliefs were burned to death. Mary Tudor was succeeded by her half-sister, Elizabeth I, who was Protestant.
Many people in England questioned Elizabeth's right to become Queen and it was believed by many in Europe that Mary was the rightful heir to the throne of England.
Her grandfather (James IV of Scotland) had married Henry VIII of England’s sister.
Henry II of France announced that Mary and Dauphin Francis were the true Queen and King of England.
In the will of Henry VIII, it had been made clear that the Stuarts (Mary, Queen of Scots' family) should not be allowed to gain the English crown.
These unresolved issues caused tension throughout the reign of Mary, Queen of Scots.