As we count the years and the generation that fought WWII pass on, then my concern for another world war go up. As long as we were reminded of the human toll WWII cost us I was not overly concern about it happening again. However, being desensitized by images of war in different media makes old photos and newsreels of the human cost of WWII and WWI less of a deterrent. So sooner or later someone will think they can actually win a war and it will happen again.
Personally I believe it will happen sooner rather than later, diplomatic and signs of respect are already viewed as being weak by a portion of the population and media in the United States.