A Library of Congress blog has a great short essay about the importance of the Magna Carta. I might copy it for my freshmen when we cover the creation of nation states next month.
The author, Nathan Dorn, reminds us that the Magna Carta "helped give birth to representative government." He also notes that the idea of taxation without representation has its roots "in a principle that was expressed both in the Articles of the Barons presented to King John at Runnymede and in chapter 12 of King John’s charter."
Thanks to my colleague, Jeff Feinstein, for sending me the link.