The calamitous nature of the violence in Syria — which has one nuclear power defending a government that has been the target of a regime change operation led by the world's superpower — combined with 2017's threats of "fire and fury" against another state intently pursuing a nuclear weapons supply of its own, has pushed the issue of a third world war directly into the public discourse.
While certain hotspots throughout the Middle East, Asia, and Eastern Europe (i.e. Ukraine) have seen some notable escalations in the last few years, a direct conflict between Russia and the United States is still yet to emerge. That's because the idea of a third world war in today's world is completely insane. If the two countries that currently possess the world's greatest supplies of nuclear weapons go to war, there may not be a world left for the victors to inhabit after the war is done, thereby making it an unthinkable proposal.