Simplify the following text for a Grade 8 native English-speaking person.
Original: Rising from a lowly page at the court of the House of Stuart , he loyally served James , Duke of York , through the 1670s and early 1680s , earning military and political advancement through his courage and diplomatic skill .
Simplified: Rising from a lowly page at the court of the House of Stuart , he faithfully served the Duke of York through the 1670s and early 1680s . This gave him military and political advancement through his brave , clever skill .