I have seen (the) Magna Carta referred to both with and without an article, a distinction that doesn't seem to have any relation to nationality (i.e. I've seen British sources and American sources both use and omit the article).
"Stop Revering Magna Carta"— The New York Times
Through Coke’s treatises, Magna Carta traveled across the Atlantic. William Penn published an edition in 1687, and in the 17th century several colonies enacted Magna Carta as part of their law. With the Stamp Act of 1765, the imagery of a tyrannical government impinging on ancient rights proved useful to both John Adams and Benjamin Franklin, who invoked different provisions of Magna Carta in calling for repeal. The founding fathers thought they were drawing on the document in drafting the Constitution, for example, in the clause “due process of law” — though that phrase was added to Magna Carta in English law only in the 14th century.
The Magna Carta enshrined our liberties – now we must fight for them again
— The Guardian
It’s because of the Magna Carta that, in 2003, 3 million of us were able to come together to protest against the Iraq war. It’s the Magna Carta that means we can legally fight cases where a severely disabled person is confined to a single room because her local council has failed to provide suitable housing. And, ironically, it’s the Magna Carta that has ultimately allowed us to vote in a government that seems hell bent on destroying it.
Is one usage preferred or more acceptable? Does the Latin nature of the phrase "Magna Carta" remove the normal need to attach an article?
Best Answer
Since "Magna Carta" is a Latin name and Latin would not need the use of an article then it is technically improper to use the definite article with it.
However, both seem to be acceptable in normal usage.
Source: http://www.oed.com/view/Entry/112237?redirectedFrom=Magna+Carta
(may need a subscription so here is the relevant text pasted in)
"Usu. without article."