In the 1950s what was an event in Africa that affected global politics during the Cold War?
Another possible event, though smaller in scale than the Suez Crisis, was the rise of the African National Congress and Nelson Mandela as a communist-supported movement in South Africa. the ANC received financial and military support from Angola and Mozambique, two Marxist countries allied with the Soviet Union. This also prompted the United States and the Western allies to support South Africa's minority white government, even though it had a policy of apartheid. This is one of the reasons why the US waited so long (into the 1980s) before it openly condemned the South African government for its racial policies. They wanted a reliable anti-communist ally in a strategic location in Africa.
I believe that the event that you are looking for is the Suez Crisis that happened in 1956.
In this episode, Egypt decided to nationalize the Suez Canal. This really worried both France and Great Britain. These countries (and especially the British) depened a lot on trade that came through the canal.
The British and French made a deal with Israel for a joint attack on Egypt. This lead to the British and French getting in a serious dispute with the United States. The US essentially forced its allies to back down to avoid a major confrontation with the Soviet Union.