Painting history was an effort and an illusion typical for the 19th century. The effort was to construct something like national myths to help a process which is now called "nation building". But the great illusion was, that history could be paintable.
Washington Crossing the Delaware, 1851 Painting from Emanuel Gottlieb Leutze, American, 1816-1868
History painting dates back to the Renaissance and was long considered to be the "grand genre". Nevertheless it has its peak in the 19th century forged by Neoclassicism and Romanticism. There it became the artistic contribution in the process of the construction of National Identities of the European and American nations.
At the same time history painting under the influence of historism pretended to be "realistic", to show history how it has been. Above all it was this pretension that led to the great failure of History painting AND Realism at the end of the century.
When artists and their public realized that telling history always will be subjective and a painting will always be an illusion Realism and history painting lost their ground to modern painting.