Revisionist history is a term used by historians that refers to a "re-interpretation" of a historical event in a way that challenges established or orthodox ideas. This is done by introducing different evidence, or by reinterpreting the motivations of people.
One of the most important dangers of revisionism is that it often has a moral component. People who use this method present a particular historical event as more or less ethical, in a way that often misinterprets the reality of the period. This is done as a way to provide more support for a particular ideology, or manipulate data to better suit a political regime. Because revisionism is often used to manipulate others, it is important to learn about this practice and challenge it, so that leaders do not easily sway people one way or another.