Over the past 500 years, these conditions have occurred sixteen times. War broke out in twelve of them. Today, as an unstoppable China approaches an immovable America, and both Xi Jinping and Donald Trump promise to make their countries ‘great again’, the seventeenth case looks grim. Unless China is willing to scale back its ambitions or Washington can accept becoming number two in the Pacific, a trade conflict, cyberattack, or accident at sea could soon escalate into all-out war. Photo credit: MIKE BLAKE – DAMIR SAGOLJ – REUTERS – ALESSANDRO0770 – SHUTTERSTOCK – ZAK BICKEL – THE ATLANTIC