In my opinion, world and national histories serve two basic purposes: to provide an overarching narrative of history and to aid the people of a nation in better understanding their heritage. These purposes present a significant challenge to the historian, but if these histories are done well, they also provide an opportunity to “make sense” of the sweep of history and provide a greater context for the many discrete people and events that make history.
World and national history are the two most challenging types of history to research and write. Because of the vast swaths of time covered, a historian must be selective about which people and events to include, or more significantly, not include in their narrative. This need to cull through material often brings out the intended or unintended biases of the author, which can also be manifested in how the history is constructed and presented. National histories are particularly susceptible to this issue, as they necessarily present history from the perspective of a particular group.
World histories also offer great opportunities for comparative history to show how different civilizations or cultures developed in similar (or perhaps dissimilar) circumstances. This presents a challenge for the author to write objectively, but it is a useful challenge, particularly for authors coming from a Euro-centric or decidedly Western point of view: “Historians confronted the very problem of accounting for the West’s position among other cultures when they wished to explain the centuries of Western dominance and expansion.”
My particular interest in comparative world history would be an examination of Chinese versus Greek and Roman military thought and development. From an earlier reading, Herodotus and Sima Qian: History and the Anthropological Turn in Ancient Greece and Han China by Siep Stuurman, we know that the ancient Greeks and Chinese had many similarities and it was interesting to discover in another class that the Chinese were writing military treatises hundreds of years before Thucydides and Clausewitz. Moreover, Sun Tzu, the best known of these authors, was just one of many great thinkers whose work is in The Seven Military Classics of Ancient China, by Ralph D. Sawyer. Clearly the Greeks and Romans were not the only innovative thinkers and a good comparative military history might give us a better perspective into Asian thought and cultural norms about warfare: “However, as interesting as they and a few books from the martial arts have proven to be, the vast Chinese military corpus-despite its historical importance and contemporary significance-remains unknown in the West.” 
Western bias, indeed.
 Ernst Breisach, Historiography: Ancient, Medieval, and Modern (Chicago, IL: University of Chicago Press, 2007), 411.
 Ralph D. Sawyer, trans., The Seven Military Classics of Ancient China, trans. Ralph D. Sawyer (New York, NY: Basic Books, 1993), xi.