The countries that were decolonialized in the postwar period were, ipso facto, decolonialized at a time when communism was a popular political ideology. Not Nordic model welfare states, not Keynesian countercyclic fiscal policy, but hard-line dictatorship-of-the-proletariat communism, the ideal of East Germany and North Korea. Zambia was a one-party state that reinvested copper profits through the disastrous program of import substitution:

https://en.wikipedia.org/wiki/Import_substitution

ISI is literally anti-economics. Rather than maximizing differential value (the production possibility frontier), ISI discourages trade and in doing so discourages exploiting the production possibility frontier. The standard example in economics of import substitution is Latin America from 1930 to 1980. The standard example in economics of failed policy is Latin America from 1930 to 1980.

The IMF's response was the horrible despotic policy of structural adjustment. Structural adjustment only ever works if the country itself is already fed up with protectionism and wants to abandon it:

http://dems.unimib.it/corsi/644/altro/dollar_svensson_ej00.p...

This is why, after the end of the Cold War, sub-Saharan Africa and Latin America have been growing, becoming more developed and less poor, and the past 20 years have been less tumultuous than the previous 40. Here's Hans Rosling with the data:

http://www.gapminder.org/world/#$majorMode=chart$is;shi=t;ly...

Look at Zambia. From 1950 to 1999 it wanders around in the left-bottom of the chart like a drunk fly. In 1999, the blue dot zooms up and to the right. When does this happen? Just eight years after Zambia's first free and fair presidential election:

https://en.wikipedia.org/wiki/History_of_Zambia#Frederick_Ch...

The Western model works. It worked in East Asia, it's working in Latin America, and humanity willing it will work in sub-Saharan Africa. And it doesn't follow copper prices:

http://www.infomine.com/investment/metal-prices/copper/all/

From 2002 to 2005, copper prices quadrupled, but there is no corresponding jump in Zambian fortunes. Rather, the Zambian economy developed at a steady pace, beginning before the rise in copper prices, influenced mainly by an improving political climate at home. Before that, Zambia hit a high-water mark in the 1960s, during the presidency of Kaunda, who began to implement socialism. It stagnated during the beginning of one-party rule and declined during (because of) the oil crisis. But mostly it was an inefficient planned economy and exhibited typical communist failure to thrive. Liberal and democratic reforms in the 90s were met with growth.

So democracy in Africa is just fine, thanks. Communism, however, sucks.

EDIT: http://minerals.usgs.gov/minerals/pubs/commodity/copper/2407...

To make this point clear, I want to give more context on the price of copper and the effect it has on the Zambian economy. Zambia's economy does not move to the right any more after 1965. But copper prices increased for eleven years after 1965, until 1976, and Zambia was unable to exploit this in a way that led to national progress. The crash around 1976-1981 clearly hurt, but not taking advantage of favorable situations hurt more.