The mighty Chinese juggernaut has been humbled this week, apparently by a species-hopping bat virus. While Chinese authorities struggle to control the epidemic and restart their economy, a world that has grown accustomed to contemplating China’s inexorable rise was reminded that nothing, not even Beijing’s power, can be taken for granted.

We do not know how dangerous the new coronavirus will be. There are signs that Chinese authorities are still trying to conceal the true scale of the problem, but at this point the virus appears...