I would be cautious then talking about a third world war in any way, shape or form to be honest. Both the first and the second word war started with regional conflicts and the causus belli of both of them were regional, it took days and months before the whole situation devolved enough for the war to become a worldwide issue.
The first one started with the assassination of an important member of the astro-hungary monarchy, so the the empire declared war against Serbia. In the case of the second one, it started with the German invasion against Poland. There were already other conflicts going, like the war between Japan and China which were added to the conflict in Europe and there was also the Chinese civil war.
Even if we could say world leader learnt something from both conflicts, still we should not underestimate the bloodthirst and stupidity of those who handle power and military capabilities in this planet.
There is another factor that I think world leaders have learned: with the development of technology as it is today, if World War III breaks out, it will mean the destruction of our earth. No one will get a second chance to start over like in the previous two wars.
To my knowledge, World War II would have been difficult to end if the United States had not been the only country to build the atomic bomb and create a huge gap in military power at that time. But nowadays, the military strength between the great powers is almost equal, there is not much difference, so attacking each other has only one result, which is total destruction. So I never thought that World War 3 would happen in our lifetime.