The old Western Confucian blog has a very good post quoting the late Russell Kirk on the origins of the Anglo-American concept of constitutional government and the rule of law: Russell Kirk on the Great Charter. Well worth a read.
As Kirk was wise to point out, and not just on this topic, American institutions and American approaches to law and politics are grounded on the English experience upon which the American colonies built. That history is part of the web and woof of our country's laws, customs and traditions. To be ignorant of that history is to be ignorant of ourselves.
If interested, here's an online English translation of the original Latin text of Magna Carta, available through Fordham University's website.