I would guess Iran. PNAC is back on the table. Russia is allied with Iran, but would probably do what China did during Korean and Vietnam wars. Israel would conveniently stay out of it, like they did before. Not sure what China would do. Probably "officially" stay out of it but offer weapons. They'd move on Taiwan, most likely. Possibly on India too, depending on what happens with Taiwan. Turkey might make some moves. It'll be a world war awful fast.
I would guess Iran. PNAC is back on the table. Russia is allied with Iran, but would probably do what China did during Korean and Vietnam wars. Israel would conveniently stay out of it, like they did before. Not sure what China would do. Probably "officially" stay out of it but offer weapons. They'd move on Taiwan, most likely. Possibly on India too, depending on what happens with Taiwan. Turkey might make some moves. It'll be a world war awful fast.