In a related conception, Gunnar Myrdal (1963: 151) thought that orthodox economic theories were “never developed to comprehend the reality of great and growing economic inequalities and of the dynamic processes of under-development and development.” This was because conventional economic theories were based on the assumption of stable equilibrium—where equilibrium, once disturbed, is reestablished by secondary changes in the opposite direction. He also thought that development analysis could not be restricted to interactions among purely “economic” variables, ignoring “noneconomic” factors. Instead, Myrdal thought, most processes exhibit characteristics of “circular and cumulative causation” so that a small initial change amplifies over time to become a substantial trend: “In the normal case a change does not call forth contradicting forces but, instead, supporting changes, which move the system in the same direction but much further. Because of such circular causation a social process tends to become cumulative and often to gather speed at an accelerated rate” (Myrdal 1963: 13). Applying circular and cumulative causation to regional growth processes, Myrdal thought that market forces widen interregional differences, causing rich regions to grow richer, and poor ones poorer. This divergence stems from two sources: “backwash effects” that retard growth in poor areas, such as a lack of external economies, a brain drain, and capital flight; and “spread effects” of momentum in a center of economic expansion, again operating through external trade, capital movement, migration, and other favorable changes that weave themselves into the cumulating social process by circular causation. Depending on which set of effects predominates in a region, the cumulative process could evolve upward, as in the “lucky” rich regions, or downward, as in the “unlucky” poor regions (Myrdal 1963: 27). In underdeveloped countries, the spread effects are weak relative to the backwash effects. In such a situation, international trade becomes the medium through which market forces tend to result in increased inequalities. In neoclassical economics, by comparison, with its assumption of diminishing marginal returns, capital would have relatively high returns in a poor region, migrating from rich regions to poor. Myrdal disputed this contention, arguing that capital is attracted to rich regions, where external economies produce increasing returns (Myrdal 1963: 28).