When relations between China and the West frayed in the wake of the 1989 Tiananmen Square massacre, Chinese leader Deng Xiaoping gave guidance that set Beijing’s course for several decades. “Hide our capacities and bide our time, be good at maintaining a low profile and never claim leadership,” he urged. As Deng and his successors opened China up to the world and avoided international conflicts, they sparked an economic miracle that propelled hundreds of millions out of poverty.

A very different attitude increasingly prevails...