The late nineteenth-century scramble for Africa saw European powers rapidly claim and formally divide up territory across the African continent, a process of imperial expansion that culminated in a conference held in Berlin in 1884 and 1885, at which representatives of European powers negotiated and formalised rules for dividing colonial claims to African territory among themselves. No African states or representatives were present at the negotiating table, despite the conference's decisions directly determining the future political boundaries of the territory being divided.
Borders drawn from distant negotiating tables, not from local political reality
The borders agreed at the Berlin Conference, and in the broader colonial partition process it helped formalise, were drawn largely according to the negotiating priorities and rival claims of the European powers involved, frequently using straight lines and other administratively convenient boundaries that took little or no systematic account of the existing ethnic, linguistic and political boundaries and communities already present on the ground across the territory being divided. This meant colonial borders quite often split a single existing ethnic or linguistic community across two or more separate colonial territories, while just as often combining groups with little existing shared political history or, in some cases, significant prior conflict into a single colonial territory instead, purely because those groups happened to fall within lines drawn according to European negotiating convenience rather than local political reality.
Those colonial-era borders became the basis for later independent states
When African colonies later gained independence, predominantly in the mid-twentieth century, the newly independent states generally inherited the existing colonial-era borders essentially unchanged, rather than redrawing them to more closely match pre-colonial ethnic, linguistic or political boundaries — a general pattern driven partly by a broader international norm favouring the stability of existing borders once independence was achieved, since attempting to renegotiate colonial-era boundaries more broadly across the continent risked opening a far larger and more destabilising set of territorial disputes. This meant many of the specific mismatches between colonial-era administrative borders and the underlying communities and political geography they cut across were carried forward essentially intact into the modern era, a documented, direct contributing factor behind a number of subsequent border disputes and internal political tensions in various African states.
What we're still unsure about
The Berlin Conference itself, the general absence of African representation in the formal colonial partition process, and the broad pattern of colonial borders being inherited largely unchanged at independence are all well documented historical fact. What's more genuinely, actively debated among historians and political scientists is precisely how much weight to assign to these specific colonial-era border mismatches, relative to many other contributing historical, economic and political factors, in explaining particular later conflicts and political tensions in specific African states — colonial border legacies are a real, well-documented contributing factor in many specific cases, but researchers continue to differ on exactly how much causal weight they deserve relative to other significant contributing factors in any given specific historical case.
This sits inside Imperialism & the Scramble for Africa, one of eight topics in Modern History, one of seven domains in History, one of seventeen subjects the app can quiz you on.