World history is not a subject; it is all the subjects. Because of this, world history as a discipline has never fit well with the traditional definition of historical research. H.G. Wells wrote the first true book of world history in 1920 and only a few authors have made the attempt to "explain it all" since Wells. In that time, world history has become the chosen subject of polymaths and possesses the most potential to unite all of the fields of knowledge. The subject of world history has developed several approaches, with "Big History" being the most modern, and flawed, of its variants.