Presenting his own interpretation of Napoleonic warfare, the author argues that the origins of modern war can be found in the Franco-Austrian War of 1809. Epstein contends that the 1809 campaign - with its massive and evenly-matched armies, multiple theatres of operation, new command-and-control schemes, increased firepower, frequent stalemates, and large-scale slaughter - had more in common with the American Civil War and subsequent conflicts than with the decisive Napoleonic campaigns that preceded it. He examines 1809 in terms of the evolving new systems of recruitment, organisation, and command used by both sides. As he shows, this was the first time that two states confronted each other on the battlefield with armies created by large-scale conscription, organised in corps, and co-ordinated along two major theatres of operation (Danubian and Italian). As a result, the opponents were forced into distributed manoeuvres that produced broad operational fronts in which battles became both sequential and simultaneous, but ultimately indecisive. Ironically, as Epstein points out, neither Napoleon nor the opposing commander Archduke Charles ever fully understood that a paradigm shift had occurred in the conduct of war. Regardless, after 1809, warfare would never be the same.