In episode one, Hillary's teacher asks what the capital of Turkey was called before the first world war. As this was set in 1930, it may be thought that it wouldn't have been referred to as the first world war, as there hadn't yet been a second world war. However the term 'First World War' was in use by 1930, with the term popularized by such publications as Lieutenant-Colonel Charles a' Court
Repington's two volume account of the war entitled, "The First World War, 1914-18", published in 1920.