Leopold von Ranke (Prussian, 1795-1886). Ranke, the father of objective historical inquiry, wrote sixty works in all, including the multi-volume studies History of the Popes, History of England, History of the Latin and Teutonic Nations, and History of Servia and the Servian Revolution. Relying almost exclusively on archival sources, he took a "just the facts" approach: "You have reckoned that history ought to judge the past and to instruct the contemporary world as to the future. The present attempt does not yield to that high office. It will merely tell how it really was."
Joseph Needham (British, 1900-1995). Needham began his colossal study Science and Civilisation in China after returning from work in China for the Foreign Office during the Second World War. Each of the seven wrist-breaking volumes comprises multiple subvolumes, so the entire seventeen-book set occupies a fair-sized bookcase. Civil Engineering and Nautics (Vol. 4, Part III) still offers the best explanation of why China led the world in oceanic exploration in the fourteenth century.
Nikolaus Pevsner (German émigré to London, 1902-1983). Already an astonishingly wide-ranging author of architectural history when he left Germany, Pevsner was appalled that there was no authoritative guide to the churches, country houses, and other architectural treasures of England. With his wife, and eventually with research assistants as well, he made up for that deficit, visiting each notable (and not-so-notable) building, county by county, over the course of forty years. The result is the forty-six-volume The Buildings of England, which mixes technical commentary with lyrical and sometimes sardonic language. (Holy Trinity Church, in Oare, "may well be considered the ugliest church in Wiltshire.") A staggering achievement.