Really? There was me thinking dictatorships based on feudal tribelines along with warlord derived power all supported by Western and now Chinese corporate interests, along with inter-tribal feuding well supported by the respective parties in the Cold War, massive population growth without support following immunisation, cultural beliefs and practices that can only be described as abhorrent, artificial country boundaries after the fall of the colonies, etc etc all contributed. Moreover there is difference between socialist systems and people who use a socialist methodology to justify their own extravagance and greed.
That is all part of it as well...
Unfortunately post decolonisation (before we had major cold war interest) all the (elected) leaders went down the socialism route, forming large government corporations (usually run by their cronies) to control things like the buying of grain/agricultural goods from farmers and the subsequent selling of that to others. That alongside the land grabbing for socialist "farms" and the forced relocation of people onto these "farms" to work in small community groups. That alongside the quashing of capitalist ideals in most new nations in favour of "spreading the wealth" and controlling it through the government caused exports to plummet, costs to rise profits to dwindle. Net exporters became net importers and the populations suffered (cost of living increased relative to wages, famine became more common etc). This knockon effect was one of the reasons for the subsequent dissent in a lot of places, with the elected officials becoming more and more mental as their tenures continued... In a lot of African nations the full scale civil wars and cold war politics occured way after this (places like Congo being exceptions to this generalness), the nations had already destroyed themselves.
I'll reccomend a few books if you're interested, it's pretty interesting, although rather depressing reading!
Unfortunately there will always be an elite in life, at least with a more capitalist, liberal society it can be a race to the top rather than a race to the bottom.
EDIT: I'm intrigued if you can name a socialist society (by that I mean nation) that actually worked. A nation where people actually live out of poverty, certainly not most of Africa, the USSR, Cuba etc...
EDIT2: Don't get me wrong a full capitalist society would be nasty but I'm very wary about the suggestion that government can do better than business in more than a few areas (Police, army etc), that includes regulation (too much or wrong).