Against all odds, we are living in a time of plenty. Neither the aftershocks of September 11 nor a tripling in oil prices has prevented the world's economy from growing faster in the last five years than in any five-year period in recorded economic history. Given recent performance and an optimistic outlook, one might have expected this to be a moment of particularly great enthusiasm and widespread support for free markets and for global integration.

Yet, in many corners of the globe, there is growing disillusion with the market system and global integration. From the failure to complete the Doha round of global trade talks to pervasive Wal-Mart bashing, from massive re-nationalisation in Russia to the increasing success of populists in Latin America and Eastern Europe, we see anxiety about the market system that is unmatched since the fall of the Berlin Wall and probably well before.

Why such disillusionment? No doubt particular factors in individual countries enter the equation. Some anti-globalisation sentiment stems from opposition to the Bush administration. But there is a more fundamental and troubling source of resistance: the growing recognition the vast global middle is not sharing the benefits of the current period of growth - that, in fact, its share of the pie may even be shrinking.

Meeting the needs of the anxious global middle is the economic challenge of our time. Two groups have found themselves in the right place at the right time to benefit from globalisation and technological change. First, those in low-income countries, principally in Asia and especially in China, that are able to plug into the global system. Low wages combined with technology and capital via financial markets have fuelled an economic explosion. It is important to remember the period between the late 18th and early 19th century in Britain was called the Industrial Revolution for a reason. For the first time in history, the standards of living of one generation were visibly and demonstrably better than the one before. In a single human life span, real per capita incomes doubled, and then doubled again. If sustained, the growth rate experienced by China during the last 30 years would lead to a hundred-fold improvement in living standards over a single human life span.

Second, it has been a golden age for those who already own valuable assets. Owners of scarce commodities have seen returns rise prodigiously. Those who own  businesses that can take advantage of globalisation to rely on less expensive labour and to sell to larger markets have seen their incomes rise far faster. Everyone else has not fared as well. Low-cost labour - ordinary middle-class workers and their employers, whether in the American Midwest or Eastern Europe - are left out. This is the reason why family incomes lag far below productivity growth in the US, why average incomes in Mexico have barely grown since Nafta and why middle-income countries without natural resources struggle to define an area of comparative advantage.

It is this vast group - which lacks the capital to benefit from globalisation and cannot compete on cost with Chinese workers - that is desperately seeking either reassurance about the shrinking world or a change in course. And yet, without its support, it is doubtful the existing global economic order can be maintained. The arguments that globalisation is inevitable and protectionism is counterproductive have the virtue of being correct - but provide no consolation for the losers.

Economists rightly emphasise that trade, like other forms of progress, makes everyone richer by enabling people to buy goods at lower prices. But this opportunity offers small solace to those who fear that their jobs will vanish. Nor can education be a complete answer at a time when skilled computer programmers in India are paid less than $2,000 a month. More can be done to strengthen protections for displaced workers. But such an approach is inevitably reactive and defensive.

In the United States and perhaps beyond, the political pendulum is swinging to the left. The best parts of the progressive tradition do not oppose the market system; they improve on the outcomes it naturally produces. That is what we need today. There are no easy answers. The economic logic of free, globalised, technologically sophisticated capitalism may well be to shift more wealth to the very richest and some of the poorest, while squeezing people in the middle.

Just as the GI Bill and domestic housing programmes after World War II were crucial parts of overall policy in the US that permitted the Marshall Plan and international financial institutions to go forward, our success in international integration will again depend on what can be done for the great middle class, at home and abroad.

Lawrence H Summers

Special to The Nation

Lawrence H Summers is a contributing editor to Opinion.