African economies boomed during the 1950s as growth and international trade multiplied beyond their pre-war levels. The insatiable demand for raw materials in the rebuilding economies of Asia and Europe and the strong growth in North America inflated the price of raw materials. By the end of the colonial era in the 1960s, there was great hope for African self-sufficience and prosperity. However, sporadic growth continued as the newly independent nations borrowed heavily from abroad.

The world economic decline of the 1970s, rising oil prices, corruption, and political instability hit Africa hard. In subsequent decades Africa has steadily become poorer compared to the rest of the world; South America experienced solid growth, and East Asia spectacular growth, during that same period. According to the World Economic Forum, ten percent of the world's poor were African in 1970; by 2000, that figure had risen to 50 percent. Between 1974 and 2000 the average income declined by $200. Beginning in 1976, the Lomé Convention and Cotonou Agreement between the European Union and ACP countries, including Sub-Saharan Africa, have structured economic relations between the two regions.
WIKI

Internal corruption and civil wars have played a far greater role in modern African economic history than the end of European colonialism. There was never any US colonialism.
An independent country must right it's own wrongs to move forward.

Another view of the causes of crisis: http://www.opendemocracy.net/democra...story_2701.jsp