With the 800 year anniversary of the signing, it is in the news a bit. It is just me, or is it being referred to differently than it had been in the past? I recall it being referred to as THE Magna Carta, but I see it referred to as Magna Carta. Has something changed, either in general or in the U.S. media, or was I just missing it?
Okay: Magna Carta, Ukraine, Eurhythmics, but still The Hague. Got it. 
Eurythmics. Sigh.
Its proper name is just “Magna Carta”. It is all about Latin and definite forms.
Ah - should’ve thought to see if the Wiki listing commented on that. Thanks! I guess I just never noticed it referred to without the definite article much before this recent wave of articles…
In Dutch, it’s called “Den Haag” and I believe that the “den” is the equivalent to “the”.
No doubt, that if Magna Carta is considered a Latin phrase, there is no "the’. But after 800 years, certainly this could be considered a term that has entered the English Language.
Things change… It used to be The Ukraine. Hell, it used to be The Lebanon.
But I agree with DrDeth: it’s an English phrase as much as a Latin one.