Hans Gottlieb Leopold Delbrück (German pronunciation: [hans ˈdɛl.bʁʏk]; 11 November 1848 – 14 July 1929) was a German historian. Delbrück was one of the first modern military historians, basing his method of research on the critical examination of ancient sources, using auxiliary disciplines, like demography and economics, to complete the analysis and the comparison between epochs, to trace the evolution of military institutions.