Historiography is the study of the methods used by historians in developing history as an academic discipline, and by extension, the term historiography is any body of historical work on a particular subject. The historiography of a specific topic covers how historians have studied that topic by using particular sources, techniques of research, and theoretical approaches to the interpretation of documentary sources. Scholars discuss historiography by topic — the historiography of the United Kingdom, of WWII, of the pre-Columbian Americas, of early Islam, and of China — and different approaches to the work and the genres of history, such as political history and social history. Beginning in the nineteenth century, the development of academic history produced a great corpus of historiographic literature. The extent to which historians are influenced by their own groups and loyalties — such as to their nation state — remains a debated question.