Lasting Effects of Colonialism in Semi Bullet Form -

New Ethnic Groups - European Imperialists and Ethnographers created or fused several different ethnic groups together in order to better rule their subjects; most famously the Hutu and the Tutsi were neatly divided into two groups out of fluid tribes and ethnic identities.

New Nations - based on European Colonialism and the artificial (as opposed to organic) borders drawn between them and other European powers in Africa - some ethnic groups were separated by borders or moved about. As a result, several African nations had to create new national identities that did not exist previously. E.g Zimbabwe, Nigeria. As a result, this produced several problems in terms of nation - building in Africa.

Dependent Economies - The economies of the colonies were exploited in order to extract resources from the colony to the metropole. Most of the infrastructure set up by the colonies was extractive in nature or designed to fulfill resource extraction. As a result, even post independence many African nations had to rely heavily on their former colonizer in order to develop its economy. In addition, many African nations had lopsided economies that focused mainly on producing cashcrops, such as coffee in Ghana, to the detriment of other agriculture. Most industrial goods or the tech needed to produce industrial goods, such as canned food, needed to come from the host country.

Weak states. Due to the aforementioned weak national identity, and dependent economies, many African states also suffered from having weak states. By the 1880s, many European states such as Britain and france had much experience in governing subjugated peoples, and used this knowledge to its full extent in Africa. Consequently, state administration and infrastructure had not been developed to the same degree as in other colonies. E.g. Nigeria in contrast with India, was governed on the cheap, and little money and resources were invested in Nigeria comparatively to India in terms of statebuilding. As a result, tax systems, infrastructure, and administrations were not highly developed. By the time independence rolled around, many governments did not have much defacto control beyond the capital area.

Chiefs - European imperialists elevated and co-opted the power of indigenous chiefs in order to rule more effectively. After independence, chiefs were more or less autonomous and could even successfully challenge the power of the state if it posed a threat to their autonomy.

Religious change - prior to colonialism most of Africa was pagan or animist, with the north being Muslim, and Ethiopia as Christian. European Missionaries converted most of Southern Africa to various flavours of Christianity. In addition, European conquest also galvanized many populations to adopt Islam or expunge syncretic beliefs. E.g. the french conquest of mali.

European rational for colonization -

Prestige - colonies were prestigious and most european countries if they could wanted colonies, even if the colonies were a money drain. See Germany in Togo. France, actually started to aggressively colonize Africa and Asia after its prestige had been severely weakened in the Napoleonic Wars and its loss of Colonies in the Americas.

Resources - African resources such as cotton were highly valued in the emerging capitalist economy. The logic was essentially of a zero - sum game - if one nation didn't colonize, then another nation could take over that area and reap the rewards. For instance, Britain colonized the most profitable areas of Africa or took it by force Ivory Coast, Kenya, South Africa, Rhodesia etc. Meanwhile France got stuck with a lot of barren desert in North Africa.

Map painting - See above. Certain imperialists such as Rhodes wanted Britain to control Africa from Egypt directly to South Africa. Consolidation of colonies also made practical sense from a military and logistical standpoint.

Civilizing Mission - Many imperialists, wanted to bring civilization and Christianity to Africa, which was seen as a dark, chaotic, violent and uncivilized continent - (these tropes persist today). As a result, they saw the great imperialist mission as a way to uplift "degenerate" races and bring them to the same level as themselves. Rudyard Kipling's the Whtie man's burden provides a poetic example of this.