When was the Second World War known as such? I believe the Great War was known by that name during the war, but I've never worked out at what point WWII became WWII.
I know the Russians knew it as the Great Patriotic War.
The name changed around 1941-1942 when the U.S. entered the war. This was also the time world war one bee known as world war one instead if the great war. If you look on the Google N gram viewer you can see a massive drop in the use of "Great War" around the time WW2 started. In case you do not know google N gram viewer takes the number if times the word is used in print so this drop of a use of the word in print can tell us people stopped calling WW1 the Great War and started using the name we know today.