This dissertation fundamentally questions the state of the field regarding militaries, state building, and narratives of modernity in the Kingdoms of Britain and Prussia. An examination of military stereotyping, common soldiers’ correspondence, religion, localism, and army reform all suggests that the British and Prussian militaries were mutually-intelligible and similar, not radically different. This similarity has broad implications for the modern history of these two European states. Britain was not on a straight road to whiggish parliamentary progress, and Prussia was not on a straight road to militarism and authoritarian rule. Rather, in second half of the eighteenth century, both of these military-fiscal states utilized their religious rural subjects, drawn from their village communities, as the basis of their military strength. Forming part of a growing scholarly revolution regarding eighteenth-century common soldiers, this dissertation relies on soldiers’ letters drawn from archives across the United Kingdom, Germany, and the Atlantic World. “The Entire Army Says Hello” demonstrates that soldiers in Britain and Prussia experienced broad similarities in their military service, and those similarities offer a new framework for the national history of these two states.