There are no positive effects.
Imperialist Europe used the 3 Cs (commerce, Christianity and Civilization) as a cover to bring death, destruction, disease and dispossesion to the “Natives”.
The so-called positive effets are part and parcel of the Civilizing Mission. The Civilizing Mission of imperialist Europe is the biggest hoax in world history.
European colonialists destroyed cities, kingdoms, empires and sultanates during colonial wars. They looted royal palaces and sacred shrines. They brought to Europe the loot of their aggression. Thousands of our works of art and artifacts now sit in colonial museums.
Millions of people were killed, worked to death or enslaved on their own ancestral lands in order enrich European colonial powers.
Imperialist Europe created a Tarzan image of Africa full of jungle static primitives and exported this image as a global brand through Tarzan movies and Tintin comic books.
The Jungle is a such a small part of Africa’s geography concentrated in the Congo Rainforest. Most of our ancestors were farmers not hunters.
Imperialist Europe made sure that the Golden Age of the African Moors, the splendor of ancient Egypt, the greatness of Axum, the caravans of gold of the Golden Kingdoms of West Africa, the advanced city states along the East African coast, the African Kingdoms who had trade and diplomatic missions in Europe and the Americas (Kongo and Dahomey), Monomotapa who had trade links with China, early Christianity in North-East Africa were erased from the narratives on African history.
We were all savages and pagans until Europeans came to civilize and Christianize us.