A foundational change or reversal in direction of a social entity either in thinking such as a scientific revolution, in political systems as in the American, French or Russian Revolutions, in economic systems as in the Thatcher revolution or in culture as in the Cultural Revolution in China is designated as a revolution.
Revolution is the moment of truth which exposes the falsehood in established structures. Revolutionaries are bearers of a righteousness not their own.
We know, however, that a revolutionary uprising – save where there is manifest, long-standing tyranny which would do great damage to fundamental personal rights and dangerous harm to the common good of the country – produces new injustices, throws more elements out of balance and brings on new disasters. A real evil should not be fought against at the cost of greater misery (Papal Encyclical, Populorum Progressio, 26 Mar 1967).