Since the late 1970s (starting with Senegal in 1979), Sub-Saharan African countries were forced to adopt free-market, free-trade policies through the conditions imposed by the so-called Structural Adjustment (SAPs) of the World Bank and the IMF (and the rich countries that ultimate control them). [...] By suddenly exposing immature producers to international competition, these policies led to the collapse of what little industrial sectors these countries had managed to build up during the 1960s and 1970s. Thus, having been forced back into relying on exports of primary commodities, such as cocoa, coffee and copper, African countries have continued to suffer from the wild price fluctuations and stagnant production technologies that characterize most such commodities. The result was often a collapse of prices in those commodities due to a large increase in their supplies, which sometimes meant that these countries were exporting more in quantity but earning less in revenue. The pressure on governments to balance their budgets led to cuts in expenditures whose impacts are slow to show, such as infrastructure. Over time, however, the deteriorating quality of infrastructure disadvantaged African producers even more, making their 'geographical disadvantages' loom even larger.
as a result of these policies: stagnation (of course)
today's equivalent of SAPs are "Poverty Reduction Strategy Papers"