Many people however believe that the failure of the Russian revolution of 1917 shows revolutions just replace one set of rulers with another. The failures of the revolutions in Nicaragua, Iran and Cuba to fundamentally change life for the workers of these countries seems to point to the same thing. A revolution essentially is a sudden upheaval in society which fundamentally alters the way that society operates or who that society is run by. It occurs when the mass of the people desire change that their rulers are unwilling or unable to grant. It can not be the result of the action of a small group of plotters.
History is full of revolutions.
Capitalism gained dominance over feudalism through revolutions, particularly the French revolution of 1789. Revolutions in countries like Cuba, Nicaragua and Iran since the second world war have had major effects on a global scale. Of course none of these were anarchist revolutions. They all resulted in the substitution of one ruling class for another. They failed to bring about classless societies.