No economic historian, however insulated from contact with economic or any other theory, can fail to notice the recent invasions of his territory by economic theorists and statisticians. Before the war theoretical economists were not, on the whole, much active in his immediate neighbourhood. Their main interests at that time centred on the trade cycle and on the related problems of the short-term equilibrium, and these could be, and in fact were, discussed against a supposedly unchanging historical background. Since the war, however, economic discussion has largely shifted to long-term problems, to secular trends, to factors of growth and decline: all of them topics very near the historian's home.

The new interest in evolutionary topics partly reflects the practical occupations of post-war economists. In the last few years they have been called upon to pronounce on at least two related issues which cannot be discussed on the assumption that time stands still. One is that of the ‘speed up’ of the industrialized economics in Western Europe, and the other is that of the ‘build up’ of the backward economics of Africa and East Asia. Both issues are concerned with growth and decline over long periods of continuous development and are to that extent ‘historical’.

Practical necessity is not, however, alone to blame or to thank for the new orientation. To borrow an adjective much favoured by economists, the invention of the ‘long-term’ theories has to some extent been ‘autonomous’, i.e. a further stage in the expansion of a developing doctrine.