When China does well, the world feels nervous. How high will it rise, and how peacefully? When China falters, the world worries. How will we manage if this mighty economy slumps, or if political control of this immense society should slip gear? Of course every big country, whether it be India, Russia, Brazil or Nigeria, generates a few such anxieties, as does the European Union, but not on the same scale. Only America has the same degree of truly global importance as China. What, for example, links the recent poor performance of Jaguar Land Rover, the halving of Tata’s profits, the shrinking exports of Taiwanese phone firms, the rescue of the Ecuadorean economy after it defaulted on debts, and the fall in the price of gold last month? The answer is the state of the Chinese market, the policy choices of Chinese financial institutions, and the decisions of the Chinese government.

Those decisions have an extraordinary ripple effect across the world. What is true in economics is also true in politics and military affairs. More than 100 Chinese ships, including nuclear submarines, last month churned through the waters of the South China Sea, firing off missiles and guns and generally behaving as if there was a war on. Planes zoomed overhead. The Chinese did this in an ocean area they had unilaterally designated as off limits to foreign ships, and they did it immediately before a meeting of foreign ministers of the Association of Southeast Asian Nations in Kuala Lumpur.

They took the precaution of announcing in advance that Asean was not a proper forum for the discussion of competing claims to islands in that sea, including the ones they have been artificially building up and equipping with air strips and harbours. True, the United States and other nations also stage war games and manoeuvres in the South China Sea. But the Chinese base their naval activities on the simple proposition that it all belongs to them, that there are in reality no “competing claims”, that the clue is in the name. It says South China Sea (or “southern sea” in Chinese) so that’s what it is. It’s Chinese. It’s theirs.

The historical arguments that China offers in support of this are fragile, but that’s not the point. The point seems to be that the Chinese government under President Xi Jinping is even more obsessed with control than its predecessors. Whether out there on the ocean sweeping aside other countries’ little navies, dealing with the problems of the Shanghai stock market by pouring in state funds, or engaging with dissidents by arresting and threatening them, this is a government that seems unable to tolerate ambiguities, differences, or, in particular, even moderate opposition.

Strange to recall that when Mr Xi came to office two years ago, he was seen by some as potentially a reformer who would bring about a more relaxed China. He has done the opposite. This is a strategy that brings many dangers. Asean ministers, for example, do not accept the Chinese line. That does not mean that China won’t prevail, but it probably does mean that it has permanently damaged its relations with some of its neighbours.

The Shanghai stock exchange crisis, which has seen the Chinese authorities dealing with equities as if they were adversaries to be battered into submission, shows the same obtuseness in a different area. China should be accommodating itself to an era of lower growth, inevitable now that its labour is dearer, but the authorities crave the prestige of figures suggesting high growth, including stocks. So it is wasting its taxpayers’ money, and eroding the rest of the world’s confidence in its economic competence, by trying to keep stock prices artificially high.

The worst effect of the all-encompassing obsession with control that Mr Xi has brought into Chinese politics is in human rights. The recent arrests of more than 200 human rights lawyers was not just an offence against human rights in itself, but a foolish capping of a vital safety valve for Chinese society. These lawyers would help if your house was illegally demolished, if officials ran off with village funds, if your church was harassed, or your wages unpaid.

They were irritating to the authorities but also useful, since they could signal where pressure was really building up. Otherwise, as one of them has written, “Suppression of moderate dissent … could explode into massive and violent social unrest.” Nobody envies the Chinese government its difficult choices. Reform is inherently risky, but so, and probably more so, is maintaining rigid control whatever the cost.