The very popular economist Paul Kurgman has been awarded The Sveriges Riksbank Prize Prize in Economics Sciences in Memory of Alfred Nobel 2008 “for his analysis of trade patterns and location of economic activity.” Here is a paper complied by the Prize Committee.
Krugman's approach is based on the premise that many goods and services can be produced more cheaply in long series, a concept generally known as economies of scale. Meanwhile, consumers demand a varied supply of goods. As a result, small-scale production for a local market is replaced by large-scale production for the world market, where firms with similar products compete with one another.
Traditional trade theory assumes that countries are different and explains why some countries export agricultural products whereas others export industrial goods. The new theory clarifies why worldwide trade is in fact dominated by countries which not only have similar conditions, but also trade in similar products – for instance, a country such as Sweden that both exports and imports cars. This kind of trade enables specialization and large-scale production, which result in lower prices and a greater diversity of commodities.
Economies of scale combined with reduced transport costs also help to explain why an increasingly larger share of the world population lives in cities and why similar economic activities are concentrated in the same locations. Lower transport costs can trigger a self-reinforcing process whereby a growing metropolitan population gives rise to increased large-scale production, higher real wages and a more diversified supply of goods. This, in turn, stimulates further migration to cities. Krugman's theories have shown that the outcome of these processes can well be that regions become divided into a high-technology urbanized core and a less developed "periphery".
From the NYT:
He has developed models that explain observed patterns of trade between countries, as well as what goods are produced where and why. Traditional trade theory assumes that countries are different and will exchange different kinds of goods; Mr. Krugman’s theories have explained why worldwide trade is dominated by a few countries that are similar to each other, and why some countries might import the same kinds of goods that it exports.
“There was something very beautiful about the old existing trade theory and its ability to capture the world in a surprisingly simple conceptual framework,” Mr. Krugman said. “And then I realized that some of the new insights coming through in industrial organization could be applied to international trade.”
Here is a talk with Krugman taken back in 2006. Read about the economies of scale and trading preferences in this paper Is Free Trade Passe. Here is a paper on The Role of Geography in Development. More links here and here.