Even without colonialism, I highly doubt there'd be an empire big enough or strong enough to unite it, especially in a post-WW2 scenario. No superpower will just sit back and let someone dominate a resource-rich continent.
For instance, how should this massive entity be united? Faith? Political party? How could they get a continent with a diverse collection of ethnic groups that won't necessarily get along well, or at all.
And then there's the infrastructure, practically some of the worst in the world. No sense trying to rule an empire that big if you can't get the trains working on time and per schedule, so to speak.