Historian Walter Scheidel finds civilization has come at the cost of glaring economic inequality since the Stone Age. The sole exception is widespread violence. Wars, pandemics, civil unrest; only violent shocks like these have substantially reduced inequality over the millennia. post
The big equalizing moments in history may not have always had the same cause, but they shared one common root: massive and violent disruptions of the established order. Reversing the trend toward greater concentrations of income, in the United States and across the world, might be, in fact, nearly impossible.
As for whether reducing inequality will ever be possible in peacetime, Scheidel simply said, History does not determine the future. Something truly innovative and original may have to happen in order to create lasting change.
See Scheidel's book, The Great Leveler: Violence and the History of Inequality from the Stone Age to the Twenty-First Century. page