Complex sentence: The reign of 16-year-old Balša III began in April 1403 when Đurađ II died of the injuries suffered in November 1402 in the Battle of Tripolje in which Đurađ II supported Stefan Lazarević to protect the throne of Serbian Despotate from Đurađ Branković.
Split into simpler sentences: The reign of 16-year-old Balša III began in April 1403 when Đurađ II died of the injuries suffered in November 1402 at the Battle of Tripolje. In this battle Đurađ II supported Stefan Lazarević in an attempt to protect the throne of Serbian Despotate from Đurađ Branković.