Modern science has demonstrated the enormous value of empirical study in testing theorems and thereby isolating the truth from everything else. Unfortunately, planned and controlled experimentation is not possible in all fields of human intellectual endeavour. For example, a theory of national governance cannot be tested in a laboratory to see whether it results in a just and happy society.
I believe that one of the principal merits of the study of history is that it reveals the closest available approximations of experimental evidence regarding political and sociological questions. The dynamics of every historical situation are highly complex and only ever partially understood, and no situation ever repeats itself in all its details - so no social theory can ever be rigorously tested for accuracy or effectiveness in one historical scenario and then applied to another with any sort of guarantee of success. Nonetheless, history provides us with the best (and only) empirical evidence that exists about humanity - in particular, about the human collective. It therefore allows us to test and improve our understanding of humanity via some of the methods that make science so reliable and successful.