Again, let us follow this tendency in economic thought to the present. These ideas were picked up and elaborated in the “new economic geography” and the “new trade theory” of the 1990s outlined by such economists as Paul Krugman, Michael Porter, and Anthony Venables. For Krugman, economic geography, or uneven regional development, is central to the process by which national economic prosperity and trade are created and maintained. Krugman’s theory differs from the Ricardian theory of comparative advantage in that he finds specialization and trade driven by increasing returns and economies of scale rather than by comparative advantage—gains from trade arise because production costs fall as the scale of output increases. In this view, economic specialization is, to some extent, a historical accident. Yet, once a pattern of specialization is established, it gets “locked in” by the cumulative gains from trade. There is thus a strong tendency toward “path dependence” (the tendency for economic outcomes to follow the path of previous outcomes rather than to rely totally on current conditions) in the patterns of specialization and trade between countries—so, history matters. An economy’s form is determined by contingency, path dependence, and the initial conditons set by history and accident. Because of forward and backward linkages, once an initial regional advantage is established, it may cumulate over time (as with Pred). However, when change in regional fortunes occurs, it will be sudden and unpredictable (Krugman 1995; Martin and Sunley 1996). Note that the Krugman model differs from that of new growth theory discussed earlier; whereas Krugman thinks that the original cause of growth in a place is relatively unimportant, emphasizing path dependence instead (that is, momentum that keeps on going), Romer stresses the role of ideas in starting and continuing a local growth process.