Ours is the second era of economic globalisation since the dawn of the industrial revolution. The first began in the second half of the 19th century and ended with a series of political and economic disasters in the first half of the 20th. If such calamities are to be avoided this time, much will depend on relations between the US and a rising China. These two very different countries will have to co-operate closely in the decades, indeed centuries, to come.

What are the chances of co-operative and harmonious relations, as pledged this week by their presidents? A start to the answer is that their similarities make the two powers natural rivals, while their differences make mutual understanding hard.