I think world wars are always looming somewhere in the shadows, waiting for just the right elements to all come together at the right time to launch it. If you think about it there are currently many situations brewing which could trigger such a thing. North Korea vs. South Korea for example. Israel vs. Iran. Somewhere in this it could be plausible to see Russia and the United States in any one of these situations—though where Russia would side is questionable.
All we can do in life is simply keep our fingers crossed. But also NOT be naive to believe it can't happen, or won't.