“China will grow old, before it grows rich” is one of those things people like to say at conferences — usually followed by a dramatic pause. The implication is that China’s rise to global dominance will soon hit a giant barrier: demographics.

China’s low fertility rate means that its population will shrink and age over the coming decades. Last week the FT reported that China’s population has already begun to fall — a few years earlier than the UN had predicted.

A large, expanding and youthful population has driven the rise of nations for much of human history. Great powers needed warm bodies to put on a battlefield and citizens to tax. Napoleon’s conquests were preceded by a population boom in France in the 18th century. By the 20th century, France’s population had fallen behind Germany and Britain; a source of justified anxiety for the French elite.