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human
[Tolkien] By what power did the Oath of Feanor compel his sons to pursue the Silmarils and carry out such crimes, even when they seemingly had the choice not to? Did the Oath itself overrule their free will and agency?

And in the end, what became of Maglor for being the only one to ultimately turn his back on the Oath? Why was he seemingly the only Son of Feanor able to break from its power?
gpt
> By what power did the Oath of Feanor compel his sons to pursue the Silmarils and carry out such crimes, even when they seemingly had the choice not to? Did the Oath itself overrule their free will and agency?

As mentioned already, Oaths are a big deal in Arda. If you break an oath, you'll be punished. Gollum swears loyalty to Frodo but betrays him anyway, and dies in the fires of Mt Doom. Androg swears to never use a bow again, breaks his promise, and is later killed by an arrow. The Men of the Mountain swear to fight Sauron, break their oath, Isildur curses them, and they die out and become the Oathbreakers. So yeah, don't take oaths lightly, and certainly don't break them. 

The interesting thing about the Oath of Feanor is that it was an unfulfillable oath due to the Doom of Mandos. Mandos lays a verbal smackdown on the Noldor, outright saying that Feanor and his sons will never succeed, and they'll only find torment and grief in Middle-earth. In a way, the Doom of Mandos is essentially the punishment for making the Oath in the first place. They were doomed to fail against Morgoth, they were doomed to turn on their own allies, and they were ultimately doomed to never get the Silmarils back. 

> And in the end, what became of Maglor for being the only one to ultimately turn his back on the Oath?

He was doomed to wander the shores of Middle-earth for, as far as we know, for eternity. This is his punishment for making the Oath and for committing evil deeds whilst following it. 

> Why was he seemingly the only Son of Feanor able to break from its power?

Well, five of the brothers were already dead. And it's less so breaking from the Oath and moreso realising that it was all for nothing in the end. Maedhros and Maglor got back two of the Silmarils, only for the Silmarils to burn them due to their evil deeds. The Oath still bound them at that point, so Maedhros killed himself, and Maglor wanders the shores in eternal pain. 

The Oath of Feanor was a very, very bad oath to make.