The simple answer is that colonialism is one major defining pieces of describing the Continent of Africa and the world in general.

To help you get a general idea of the colonial impact on Africa, I would recommend reading the African FAQ

The colonial powers touched nearly every aspect of the continent: set boundaries bought and sold people via the intercontinental slave trade and forced labor; tore down social hierarchies and introduced new religions and languages; founded schools that taught histories created by the colonial powers and introduced racial thinking into social groups. Mines were dug and valuable metals were extracted, rivers were damned or rerouted, the suez canal was dug through it; You had immigrants from Europe, the Middle East, and Indian subcontinent.

And when the colonial period was over, governments would assassinate, or undermine democratically elected leaders and prop up dictators. They would install trade agreements and would control development projects. Christians and Muslims. Countries would be held under the sway of the international community with crippling debt.

Colonialism not only shaped Africa but it also shaped the developed world. The Americas would be unrecognizable without slavery, and Europe would never have been as powerful if they hadn't extracted so much wealth from the rest of the world.

Since the effect of colonialism both created Africa in a modern sense, and it continues to directly affect Africa today, it is critical to appreciate the historical forces acting on policies that are being made today, and using it to inform current decisions. It is fascinating how events that started happening hundreds of years ago can directly affect how people not only see their continent, but in how they see themselves and their own identities. Removing Africa from the context of colonialism would be just as cataclysmic, so you have to appreciate what happened and look for openings about how navigate a post colonial reality in which the African people are allowed to control their own destiny and can have the rest of the world be in equal partnership.