When James V died on December 14, Mary Stewart was just six days old. She would become Queen of Scotland, but the country was ruled by a series of regents, with her mother taking control of her possessions when she was two years old.
England and Scotland were still at war, but Henry VIII wanted peace. When a Protestant became the regent of Scotland, the English king took the opportunity to suggest a marriage between his son and the Scottish Queen. It led to the Treaty of Greenwich, which had a few clauses within it—favourable to the Scottish and the English. One of the biggest clauses was that if the marriage came to an end without issue, the two countries would become separate again. They were still separate entities legally.
However, the Catholic Cardinal Beaton took over as regent in 1553, and brought a pro-French, Catholic regimen to the country, something that angered Henry VIII. It led to the treaty dissolving in December of that year, and the betrothal was off. England and Scotland were back at war.
To keep Mary safe, Scotland turned to France for help. After that, she was sent to the French court and betrothed to her future first husband, the Dauphin Francis. Henry II of France became like a father to the five-year-old girl, and she grew close to her future husband. In fact, when both Henry II and her husband died about a year within each other, she was distraught.
She was raised as a French Catholic, and loved her religion. However, it caused problems when she moved back to a Protestant Scotland.