I don't see a WW3 happening in the manner of the previous two World Wars - nations against nations, fighting on wide fronts for land, resources and people. The shape of the world doesn't fit that concept any more. There will be (as there always have been) ongoing localised conflicts which will be part of wider power struggles but it's in not in the interest of anyone with influence to escalate to wider scale conflicts.
To be honest, I don't really think anything has significantly changed throughout the modern era. The World Wars were quirks of history, sequences of fairly local events combining in to something larger at random rather than by any intent. It could even be argued that WW1 was "just" a European conflict that dragged in the colonies of the European Empires and WW2 was really two separate conflicts - Europe/North Africa and the Pacific - so not really a world war either.
I think the weakening of the super-powers of the past, globalised communication and the virtualisation of many resources makes that kind of thing very unlikely on a world-wide scale.