The most likely is WWIII involving Russia and parts of Europe first.
Oil has fired the first shots. Have you seen Putin landing a 200 pound halibut lately? He has to do something to keep his country's mind off the economy.
The US gets dragged in. China tried to stay out but then can't resist a jab at Taiwan while we are occupied with Europe and decide if they are already that far, might as well take a bit of revenge on Japan for WWII.
It will at least be interesting. They always say may you live in interesting times. I was getting a bit tired of tweets and texting anyway. A few well placed EMP should fix that problem right up.