In the more centralized states of early modern Europe, rulers exerted greater control over warfare. They established ransom, parole, and exchange for all ranks, not simply the elites. Men taken in battle and held by enemy forces could be ransomed by the states for which they fought. In certain circumstances, prisoners could be free of confinement until ransoms were paid, a new sense of parole. Prisoners could also be exchanged between warring parties. The details of these practices were set out in formal agreements, “cartels,” between adversaries. State surrenders in European wars were set down in treaties; however, the language of the treaties was typified by respectful treatment of the defeated, avoiding the term “surrender,” and praising the return of peace. Moderate language conformed to the principles of an age in which contemporary writings praised the more civilized, even polite, conduct of war. Surrender of military units was common, particularly in siege warfare. The besieged could win advantages by surrender. Garrisons might be given the honors of war, by which a defeated garrison would be allowed to march out and proceed to a friendly camp or garrison, rejoining their own army and escaping imprisonment.

This chapter opens the first part of the book that presents the background of the First World War. It deals with the emergence of the concept of “enemy alien” in the debate among international lawyers. Starting with the Law of Nations published by Emer de Vattel in 1758, it analyzes and discusses what the foundational texts of international law in the century-and-a-half preceding the First World War said on the rights of foreigners in peacetime and on the conduct toward these same foreigners when they became enemies in wartime. It then compares legal doctrines and practices analyzing the behavior of belligerents towards enemy aliens in a string of interstate wars that occurred between the end of the eighteenth century and 1865, namely the French Revolutionary Wars of 1792–1793, the Napoleonic Wars, the War of 1812 between Britain and the United States, the Crimean War and the American Civil War. The chapter follows the changes in the attitude toward enemy aliens that mass conscription and the post-French Revolution concept of citizenship and nationality triggered.