War Horse is based on the novel by Michael Morpurgo, a solid young adult novel with classic status in the UK. It was turned into a brilliant bit of theater (really, you should see it if at all possible). But Spielberg's film fails on every level.
Filmmakers and novelists have long been fascinated by the way the optimistic, sunlit, pre-1914 Europe of emperors in plumed helmets and hussars on parade so quickly turned into a mass slaughterhouse on an unprecedented scale.
Many years ago I wrote a screenplay called The War Horses. My story, telling how the Boer War of Africa was won on a ranch in the American West, was based on a document discovered in the University of Denver's library.