When did World War 2 start being called a "world war" and when did it start being called World War 2? Thurber's The Last Flower (copyright 1939) makes reference to World War 12 so I'm curious as to whether he invented the sequential numbering of wars. According to Wikipedia, the book was published in November of 1939 (so one would assume it was written earlier) and the conflict in Europe was still relatively young and had not developed into a "world war" yet.

Another Wikipedia page says that WW1 "was predominantly called the World War or the Great War from its occurrence until the start of World War II in 1939, and the First World War or World War I thereafter." But there is no citation so I don't know if Thurber was following a convention within 2 months of the invasion of Poland or was creating a system of naming wars that others then followed.