Hey, let's not be closed-minded here, it could easily be all the powder kegs at once.

WW1 wasn't a single-issue. WW2 wasn't a single issue. China and Japan didn't give one fuck about how blondes with big noses and with little noses hated each-other. They had multiple issues all around, that conglomerated into factional sides over time.

A "WW3" scenario, or a collapse scenario, likely the same thing, will likely be a very rapid domino chain of questionable origin point.

Wild Prediction Example: US has some form of nation-wide mass unrest in early 2025 over election results. Seeing the unrest, China makes a land grab. Seeing China do it, Russia quickly follows suit. The dual land grabs and subsequent political upheavals send refugees into the EU, overstraining and collapsing their system in mere months. Seeing these disasters on the world stage, the unrest in the USA becomes a "if my side isn't in power, the world is destroyed" level unrest and spawns a civil war.

These types of powder kegs don't tend to go off on their own. This isn't a powder keg, it's an entire fireworks factory of disasters.