Once in a while I get cornered by a bitter and twisted resentful Dutch person demanding "what's so great" about Britain.
My initial response is "what's so great about your understanding of English"?
So many people think that the word "great" in this context is some kind of arrogance. It isn't. It doesn't mean "we're so ****ing great and you're not"...
...the word great has several meanings =>
great - definition of great in English from the Oxford dictionary
In the context of a land mass great just means large or the larger part of - see definition 1.3 in the link above.
At the moment GB (the abbreviation of Great Britain) is used on every "euro" number plate. It is still in common use although because a large part of the non native English speaking population on planet earth thinks we're being arrogant, in our use of the word great, often the misnomer "united" is used.
We're not united and there's very little kingdom left!