After World War II, the world saw large-scale decolonization as European countries no longer had the will or means to maintain control of their colonies and suppress independence movements. While advocates of independence had great hopes for the futures of their countries after decolonization, not all those hopes were realized.
The first problem was that the borders of various new states were drawn with little regard to what might make a country successful, often encompassing groups of warring tribes, opposing religions, or different ethnic groups. This lack of a cohesive basis for nationhood led to factionalism or even civil wars in newly freed countries.
Next, many of the newly independent countries lacked the institutional structures needed for success. Precolonial forms of government and leadership had been destroyed by the Europeans, and when the Europeans left, often rebuilding institutions was difficult. Sometimes the only groups to step into the resulting power vacuums were a small wealthy European-educated elite or kleptocracic warlords. Economic power, especially in countries such as Zimbabwe or South Africa, often remained in the hands of a limited group of white settlers.
Finally, many of the freedom fighters who took power after the departure of the Europeans were not really prepared to make a transition to democratic rule. Some were powerful members of ethnic groups who oppressed minorities and instituted governments that were basically a way of giving handouts to their own communities rather than rebuilding nations as a whole. Others were military strongmen. Even those with good intentions often lacked a strong civil service and other necessary institutions for successful governance.