Amid the avalanche of summer reading crashing on to my desk falls another hefty tome about China’s re-emergence as a global power.

The theme is familiar: the present century will belong to Asia in general and to China in particular. The book’s title, When China Rules the World, permits none of the doubts and vacillation about the future course of events that often afflict this columnist.

By unhappy accident, publication has coincided with the most serious unrest since the Cultural Revolution, in China’s Xinjiang province. More than 150 have been killed in ethnic clashes. Hu Jintao, the Chinese president, this week felt obliged to cancel his appearance at the Group of Eight summit in Italy to fly back to Beijing.

Skipping a gathering of some of the world’s most powerful politicians was no small thing for the leader of a regime that that places a high premium on the image it shows the rest of the world. Yet it was also a reminder that China’s politicians are rarely quite as confident as western observers about their country’s destiny. In my experience, the west’s awe is as often as not matched by China’s anxiety.

We should perhaps not blame the author of this latest book for the cover. As far as I can tell it has become a rule of modern publishing that serious books are no longer allowed serious titles. The marketing people rule: to find space on the bookshop shelves any new publication must shout a single message – the louder the better. There is no room here for ifs, buts or maybes; equivocation is for wimps.

In this instance, the publisher is not alone in its certitude. Martin Jacques, the author, is somewhat more nuanced in developing the argument than the title allows, but the central thesis is much as advertised. Within a few decades China will be the pre-eminent world power and, to borrow from the sub-title, the inexorable rise of the Middle Kingdom will mark “the end of the western world”.

Such bold, but not infrequent, claims make one convenient assumption and one big mistake. The convenient assumption is that if events turn out otherwise most people will have long forgotten the original hypothesis. Failing that, there will be another book to be written to explain why things turned out to be otherwise.

Thus back in the 1980s a clutch of distinguished scholars proclaimed that a rising Japan would soon supplant the US as the world’s leading economic power. Japan promptly fell into a decade of slump. More recently, there were equally certain forecasts that the US was destined in perpetuity to be the world’s hyper-puissance. The pity was that George W. Bush fell for the propaganda. Then, of course, there was the famous claim that the collapse of communism marked the end of history. To my mind, recent times have felt rather more like the beginning of history, but Francis Fukuyama’s career has not suffered for predicting otherwise.

The big mistake is to assume that the future can be mapped out in linear progression from the present. The Chinese economy has been growing at something close to 10 per cent a year for 30 years. If it continues to expand at that rate it will quite soon overtake the US as the world’s biggest economy. Case closed: Beijing will rule the world.

To talk of China as a great power is uncontroversial. Even allowing for interruptions, the economic trends suggest that sometime in the first half of the present century China will indeed join the US as a superpower. The success with which China has weathered the global financial storms of the past year has rightly hardened this view.

Nothing, though, is pre-ordained. If there is a lesson to be drawn from the recent past it is that geopolitics does not travel in straight lines. Yet the breathless extrapolations from China’s rise paint a picture not just of a great power among several but of one whose writ will soon run across the globe. Asia, we are told, will be China’s fiefdom, Africa its source of raw materials, and Latin America its client. Things may turn out that way; but the future is just as likely to be otherwise.

The sense I have taken away from successive visits to China in recent years is that policymakers there feel this uncertainty much more acutely than their western cheerleaders. This week’s images from Xinjiang of violent clashes between the indigent Uighur population and immigrant Han Chinese speak to the fragile social order that preoccupies, and unnerves, many of its leaders.

Even as outsiders anticipate China’s global power, Mr Hu and his colleagues worry that the prize could be lost to the internal instability of rival nationalisms and ethnicities. Beijing’s response to such tensions has long been repression. But as in Tibet last year, so in Xinjiang this. Putting troops on the streets may calm the immediate unrest – albeit at considerable cost to China’s international standing – but it is not a long-term answer. The demands of Uighurs and Tibetans for greater self-government cannot be wished away by swamping the country’s far western provinces with Han Chinese migrants.

The social tensions reach beyond the ethnic. For all that China’s prosperity has risen tenfold within a generation, hundreds of millions of its citizens still live in the countryside on a dollar or less a day. The new order must accommodate its economic aspirations just as the prosperity of the urban middle classes creates demands for a more pluralist framework for politics.

Policymakers in Beijing are acutely aware of the threat these trends pose to the status quo. They are at once obsessive in their defence of China’s “national integrity” and angrily dismissive of suggestions that they should mimic western political structures. Yet they are also aware that the autocracy and corruption on which the present system rests will not withstand the pressures of economic and social change.

Only the other day Mr Hu called for a “vigorous improvement” in democratic decision-making to help fight corruption within the ruling Communist party.

The story of China over the coming decades will be whether, and how, it manages to create a system of politics that can sustain social cohesion alongside rising prosperity. It may succeed and thus emerge one day as the world’s pre-eminent power. But, for all the simple certitudes beloved of today’s publishing industry, there are some very big “ifs” along the way.

– Philip Stephens