I am writing this in Xi’an, ancient capital of the Chinese empire. This is where the famous terracotta warriors were found, mute witnesses to the scale, resources and organising capacity of the ancient Chinese state. Xi’an is a city of 8m, in the middle of the country. The road from the airport is surrounded with half-finished buildings, a sign of the construction boom of recent years. The economic changes are palpable, as they are elsewhere in this vast country.

China is a nascent superpower. According to the wonderful database published by the Conference Board, its gross domestic product, at purchasing power parity, was 80 per cent of that of the US in 2009. Its GDP per head has risen from a mere 3 per cent of US levels in 1978 to close to 20 per cent in 2009.

By 2014, at current rates of relative growth, China’s economy will pass the US, in absolute size, to be the biggest in the world, at PPP. Its GDP also seems almost certain to surpass that of the US at market prices before the end of this decade, partly because of its rapid growth and partly because of the inevitable appreciation of the renminbi.