This account of the National Army during the Irish civil war tells its story from the divides created in the Republican movement by the Anglo-Irish Treaty to the development of a new military organisation capable of upholding the Treaty provisions and facilitating the establishment of a new state. The National Army is largely overlooked in modern studies of both the Irish Defence Forces and the IRA. Its brief two-year existence helped lay the foundation of a new Irish state, but its broader legacy has been shrouded in generalities and controversy. Through a detailed analysis of its formation, structures, recruitment profile and operational capabilities, the book seeks to shed light on areas previously overlooked including Free State military casualties, the process of mass recruitment and the wider role of the military within the new Irish Free State. This book is aimed at academic historians, postgraduates, undergraduates, local historians and those with an interest in military history and the wider Irish Revolutionary period. As the National Army was recruited from an all-island basis, it will also have popular appeal to readers across Ireland and throughout the Irish diaspora.