Think WW2 was only a world war if you were one of the English speaking countries of the world (or relatively close allies). Otherwise, you were fighting the same guys you've been fighting for the last 2000 years (Germany/Huns Vs Soviets/Slavs, Japan V China).
But both WW1 and WW2 were inevitable in some form. WW1 was about the end of Monarchies. Between 1910 and 1920, something like 40% of the world's population lost their previous ruling govt. method (which they had for upwards of 5,000 years). Pasha Bey, Hollerhotzen, Romanoffs, and Austo-Hungarian Crowns all fell in a time period of a couple of years. Toss in the end of the Chinese (in 1910) and you're looking at a huge event. Most of those family rulers lost their crowns in the first world war (not much of a global war in terms of fighting but definitely global in terms of effect).
The Second World War was a combination of competition in ideologies (Nazi v Communist), centuries old grudges (Slavs, Huns, Franks, Anglo-Saxens), new players on the scene (North Americans, Austrialians, South Americans) and the final toll on the Monarchies that had escaped the first bloodletting that ended in 1920.
By the time WW2 was over, the Monarchy as an effective system of govt was essentially dead. Only in small, out of the way places did it survive as a form of govt (with the king/queen doing more than being a titular head). Communism and Democracy had arisen as the majority forms of govt in the world. Communism collapsed under the weight of it's own inequities.
Democracy, on the other hand, is still alive but evolving. It's future forms will be the question. Another question still unknown is will a modern democracy attack another democracy? In the modern era, it has never happened (happened in ancient Greece all the time, but that was their gig). It will be interesting to see where that idea goes when resources get scarce.
But anyhow, the First World War was about the death of kings. The Second was about the rise of the populist political systems.
IMHO.