The World War began on July 28, 1914. This separation of the same conflict into two different wars has always struck me as being pointless - "this is not a peace treaty, it is an armistice for twenty years." Moreover, all of the smaller European wars that took place in the 'interwar' period - the Spanish Civil War, Abyssinia, etc. - are basically also continuations of the First World War, and have their roots directly in the aftermath of the Armistice.
A words of Marshal Foch
Yeah. I've never especially appreciated the fact that World War I is basically shunted to the backburner in any discussion of the last century of history, particularly when I find it to be the most interesting era of the last century: rather than a simplistic conflict of absolute good versus absolute evil (in the popular mind, at any rate) as World War II is, one actually has to know a little something to understand its predecessor. Moreover, it gave rise to perhaps the most culturally fertile and culturally bold period in European history - Weimar Germany.
Hey that's why Star Wars is so popular... and the Lord of the Rings movies. And the Iraq war (at least in the beginning, when it was still popular in the U.S.). No shades of grey please! It tends to confuse people.