Complex sentence: The Scots allied with France, who sent reinforcements for the defence of Edinburgh in 1548, while Mary, Queen of Scots, was removed to France, where she was betrothed to the dauphin.
Split into simpler sentences: The Scots allied with France, who sent reinforcements for the defence of Edinburgh in 1548. The Queen of Scots was moved to France, where she was betrothed to the Dauphin.