Published in 1980, Michael E. Porter's Competitive Strategy went against the accepted wisdom of the time that said firms should focus on expanding their market share. Porter claimed they should, in fact, analyze the five forces that mold the environment in which they compete: new entrants, substitute products, buyers, suppliers, and industry rivals. Then they could rationally choose one of three "generic strategies" - lowering cost, differentiating their product, or catering to a niche market.
Because the potential returns appear to be greater in poorer countries than in the developed world, modern economic theory implies that rich countries should continually invest in poor countries until returns balance out. In fact, this doesn't happen. Economist Robert E. Lucas Jr. asks why in his groundbreaking 1990 article, "Why Doesn't Capital Flow from Rich to Poor Countries?" The question has become known as the Lucas paradox. Lucas analyzes this, focusing especially on the role of human capital.