In the 28 July 2012 issue of New Scientist, there is an excellent article on why anthropologists believe the human race, after 50,000 years of relative equality, became very unequal in the last 5,000 years; resulting in today's 1% owning up to 20% of the total wealth.
The reason they believe was the root cause of this trend is the surplus that started to build up once mankind changed from nomadic hunter-gatherers to settled farmers. Those who accumulated most were able to lord it over their less fortunate village mates. Soon hierarchies of chiefs and super-chiefs and kings and emperors evolved.
Later, in the European middle ages, religious and political power gradually changed hands and the merchant classes started to rule the roost - at least as far as wealth is concerned. Fighting wars was and is not cheap and the one constant beneficiaries were and are the banks and bankers. So today's top 1% includes not only land and other asset owners of the past, but also builders and manufacturers and, surprise, surprise, bankers and other financiers.
For more information on inequality, read: http://en.wikipedia.org/wiki/List_of_countries_by_income_equality