Tolkien wrote in more than one of his letters (which you can get here: https://www.amazon.com/Letters-J-R-R-Tolkien-J-R/dp/0618056998/ref=sr_1_1?ie=UTF8&qid=1499166870&sr=8-1&keywords=letters+of+jrr+tolkien) that one of the main themes of his Silmarillion and Lord of the Rings was death.  In this video I discuss the background for the them, its general implications, and some specific storylines where it comes into play.  My video on another theme, sub-creation, is here: https://www.youtube.com/watch?v=HOpbrkRe3QY