Reading contemporary histories of the First World War, I noticed that at the start the nation in the Balkans is referred to as Servia, but in numbers published after the back half of 1916, it has turned into Serbia.
Is there any particular reason for this?
Consulting Google NGrams gives:-
which seems to correspond to my observation.
Edit Replaced Google NGram with version using capitalised names, as suggested by Steven Littman; the result makes rather more sense.