The part of the sentence that tells "who" or "what" the sentence is about is the subject.
Answer:
<u>In spite of</u> her beautiful voice, she didn't want to be a singer.
Edited passage (corrections are in bold, everything else is fine):
Considered one of the most significant documents in the history of the democracy, the Magna Carta was written by thirteenth-century barons to protect their rights against King John of England. During the American Revolution, the document inspired the colonists in their pursuit of freedom.
Hope I was able to help! Feel free to leave a comment if you have any further questions :)
