Decolonisation saw dozens of former colonies across Asia and Africa gain formal political independence within roughly two decades after the Second World War, dismantling colonial empires that had, in some cases, stood for well over a century. That rapid wave of independence didn't happen from any single cause; it resulted from a genuine combination of forces, organised local independence movements, colonial powers left economically and militarily weakened by the war, and a shifting international climate that made continued colonial rule considerably harder to sustain or justify than it had been before.
Local independence movements provided organised, sustained pressure from within
Across colonised territories, organised independence movements, often building on decades of earlier political organising, mobilised genuine popular support and applied sustained pressure on colonial administrations, through negotiation, civil disobedience and, in a considerable number of cases, armed struggle. These weren't simply spontaneous uprisings; many were led by figures and organisations with real, developed political programmes and, in several notable cases, decades of prior organisational experience, which gave the postwar independence wave a level of sustained, coordinated pressure earlier anti-colonial movements had often struggled to maintain.
A weakened, discredited colonial order made that pressure considerably harder to resist
The Second World War left major European colonial powers economically exhausted and militarily stretched, considerably less able to maintain the costly military and administrative presence colonial rule had traditionally required, while the war's own rhetoric of self-determination, and the discrediting of doctrines of racial hierarchy the war had helped by association, made colonial rule considerably harder for those same powers to justify internationally. This confluence of weakened material capacity and eroded international legitimacy is exactly why decolonisation moved as quickly as it did across the postwar decades, rather than unfolding as gradually as earlier anti-colonial movements, facing colonial powers still at full strength, generally had.
What we're still unsure about
That local independence movements, weakened colonial powers and a shifting international climate together drove the postwar decolonisation wave is well established, extensively documented history confirmed across dozens of individual national cases. What's more genuinely a matter of ongoing historical debate is exactly how much relative weight to assign each of these three factors for any specific country's path to independence, since the balance between organised internal pressure and external colonial weakness varied considerably from case to case, and historians continue to actively debate that balance for individual territories rather than treating decolonisation as a single uniform process that unfolded the same way everywhere.
This sits inside Decolonisation & Independence Movements, one of seven topics in Contemporary History, one of seven domains in History, one of seventeen subjects the app can quiz you on.