If you define a World War as all the major powers in a war with each other or as a part of an alliance, then we have actually had 7 world wars:
30 years War
Spanish Wars of Succession
Seven Years War The Napoleonic Wars
The Franco-Prussian War
WWI
WWII
If you look at the timeline they are about every 50 years. So we are over due for the last peace to no longer be relevant by new events.
What could be some of those events?
China becoming a military power comensurate with its population or Japan becoming a military power comensurate with its economic power.
In this case one may bring the other.
I think the Chinese are building their navy as a ‘just in case’ scenario if the world goes up in flames because of Islamic terrorism. I remember the article that said they were planning on moving into Somali waters to deal with the piracy issue. Also, after WWII, the Chinese are testy about Japan and after colonization, they want to be able to prevent any and all foreign interference, militarily if need be.