"History is written by the winners"
However, just like science, history is not a static subject. What was thought to be true 101 years ago is not necessarily going to be true forever. History is not written in stone.
As more information and documets are uncovered, discovered and past secrets are declassified, new facts and viewpoints emerge to give us a wider understanding.
This mustn't be confused with "revisionism" as in the sense of Holocaust deniers, who attempt to deny history, contrary to a massive body of overwhelming evidence in order to push their own sick beliefs, in a similar way to how Creationists deny the enormous weight of scientific evidence about Evolution and Natural Selection in order to push and enforce their own agendas.