Complex sentence: The throne became vacant with the sudden death of Emperor Zhengde in 1521 and the 14 year old Jiajing was eventually chosen to become emperor and relocated from his father's fief to Beijing.
Split into simpler sentences: The throne became vacant with the sudden death of Emperor Zhengde in 1521. The 14 year old Jiajing was eventually chosen to become emperor, and so relocated from his father's fief to Beijing.