This week's Anglo-American historians' conference in London aims to take on the world. Alan Mcafarlane charts its trends

It is always worth looking at the development of theoretical systems from the outside. Imagine how an Asian observer might summarise changing approaches to world history advocated by western theorists over the past 500 years.

They might note that, until the 17th century, time was roughly conceived of as circular. There would be temporary "progress", but ultimately one would "return" to the same position - to the Second Coming, the re-birth, the bottom of the wheel. Then, in the 18th-century Enlightenment, time was increasingly conceived of as a line rather than a circle, progressive, upward-moving. Many western thinkers believed mankind moved through "stages", linked to the mode of economic production.

Briefly shaken by the French Revolution and the obvious miseries of early urban-industrial society, faith in progression revived after the 1830s, launching the full-scale Victorian progressive evolutionism which peaked between about 1860 and 1880. Marxism, Whig history and reborn anthropology and sociology developed as man's history was increasingly seen as a long upward ascent along moral, mental, material and other dimensions.

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Fading at the turn of the century, this phase was buried in the horrors of the first world war. From the 1890s talk was either of long cycles again - Spengler and Toynbee - or of functional stasis. Many thinkers were deeply averse to talk of long-term, inevitable improvement. Lasting in many countries until after the second world war, this view continued in the new intellectual fashion, structuralism.

Then, as the wounds of war healed, optimism grew. This found expression in revived Marxism, the work of W. W. Rostow, the triumph of capitalism as described by Fernand Braudel, or cultural materialism in anthropology. During the past 20 years all these different trends have mingled. Theorists are now deeply divided. At one extreme are those such as Max Weber, Isaiah Berlin, Ernest Gellner and E. L. Jones, who believe that mankind's development is uneven, unlikely and fraught with the perils of chance, contingency and non-inevitability. The riddle for them is that man ever "escaped" from agrarian civilisation at all. In the other camp are those who, like Francis Fukuyama in his End of History, believe that the collapse of the Soviet Union and the extraordinary growth of Asia show there is no puzzle about "progress". It is inevitable, just a matter of clearing blocks off the runway and allowing societies to "take off". Man's ingenuity and creativity and the mighty power of technology will lead us ever upwards. Capitalism and democracy have triumphed for good.

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The Asian observer might point out that these changing paradigms appear to shadow political relations and the rate of economic progress. In periods of rapid economic and technological growth, especially when linked to political dominance and expansion by a certain civilisation, confidence rises and optimistic, "progressive" and teleological theories dominate. In periods of political confrontation, non-progressive moods prevail.

This is why the present situation is so fascinating. The rapid economic development of much of Asia undermines western confidence in its own destiny. But the Asian boom and the collapse of Soviet communism feed belief in the inevitable progress of mankind. What is not in doubt is that the over-arching paradigms within which historians work are affected by these global changes in power and economic and technological growth.

* This article is based on a paper titled "The Riddle of the World" delivered at today's Anglo-American Conference of Historians. Alan Macfarlane is professor of anthropology at the University of Cambridge.