In This Article Expand or collapse the "in this article" section Mercenaries

  • Introduction
  • General Overviews
  • International Law
  • Morality

Military History Mercenaries
Sarah Percy
  • LAST REVIEWED: 19 July 2023
  • LAST MODIFIED: 24 July 2013
  • DOI: 10.1093/obo/9780199791279-0105


Mercenaries, often referred to as the “world’s second-oldest profession,” have been part of the history of war since its beginnings. While their precise description has varied over time, generally speaking, mercenaries are fighters who are not members of the group that hires them (whether that group is a state, a city-state, or the followers of a feudal lord) and are usually motivated by financial gain (although this feature varies over time; the idea of motivation by financial gain makes little sense as a marker of a mercenary in the medieval period). This article focuses on mercenaries in the postclassical period, although there is an extensive literature on mercenaries in classical Greece and Rome. Moreover, the article focuses on mercenaries within the European tradition of war, as the use and impact of mercenaries are both extensive and distinct in the European context. Finally, this bibliography focuses specifically on the long lineage of entrepreneurial mercenaries (whether or not the entrepreneur was the leader of a band of mercenaries or a leader of a state selling mercenaries to another state). Other forms of foreign service, including permanent subsections of the state military relying on foreign recruits (such as the French Foreign Legion) and volunteers (such as those in the Spanish Civil War or mujahideen in Afghanistan) also exist but are beyond the scope of this article. Mercenaries have been hired by a variety of actors in order to supplement existing forces and/or to provide specific expertise in military tactics or technology. They have shifted from individual entrepreneurs able to sell their services to the highest bidder, either in groups or singly. This form of entrepreneurial mercenary was common roughly between the 12th and 16th centuries, and was gradually replaced by a more organized system, whereby states took control of the mercenary trade and bought and sold soldiers from one another, a system that began around the 15th century and ended after the Crimean War in the mid-19th century. In the 20th century, mercenaries reappeared during the wars of decolonization in Africa, again as entrepreneurial individuals, nearly always fighting against the interests of newly decolonized states. In the late 20th century, private military companies appeared in conflicts in Angola and Sierra Leone. These companies sold a broad range of military services, including providing combat troops. They have disappeared and been replaced by private security companies (PSCs), which again provide a variety of military and military support services stopping short of combat. PSCs appeared in large numbers during the conflicts in Iraq and Afghanistan. There has been surprisingly little written about mercenaries, particularly pre-20th-century mercenaries, as a category on their own, separate from studies about the overall organization of war in a given period. However, a number of these broader accounts of military organization are a good introduction to mercenary use, and they are featured throughout.

General Overviews

There are surprisingly few general overviews of mercenaries over a broad historical period. Most accounts focus on mercenaries in a particular era. Mockler 1969 provides a general history of mercenary activity from the medieval period through to mercenary involvement in the wars surrounding African decolonization, ending in the early 1970s. Mockler 1985 summarizes in great detail the pre-19th-century material in a chapter and examines the use of mercenaries in Africa, carrying the analysis through to the mid-1980s. Percy 2007 examines mercenaries from the 12th century through private security companies in 21st-century Iraq but does so with an explicitly international-relations focus, arguing that decisions to use private force have historically been influenced by a norm against mercenary use. France 2008, an edited collection, provides a very clear overview of medieval mercenaries, considering cases from a wide geographic spread and temporal period. Kiernan 1957 provides an in-depth examination of mercenaries in European armies, linking the use of foreign fighters to the development of absolute monarchy. Parrott 2012 examines the use of private enterprise to fight wars throughout early modern Europe, including during the Thirty Years War, arguing that the use of state-recruited and state-administered militaries is anomalous in European history. Thomson 1994 focuses on the use of force by private actors in general, considering mercenaries alongside privateers and mercantile companies. Her main concern is the manner in which the state monopolized the use of force externally by controlling these actors, having first achieved an internal monopoly on the use of force. Singer 2008 provides a very broad overview of the history of mercenary use and its evolution into the private military and security industry.

  • France, John, ed. Mercenaries and Paid Men: The Mercenary Identity in the Middle Ages; Proceedings of a Conference Held at University of Wales, Swansea, 7th–9th July 2005. Leiden, The Netherlands, and Boston: Brill, 2008.

    DOI: 10.1163/ej.9789004164475.i-415

    This edited collection extensively covers the medieval period, throughout Europe, from the 12th to the 16th centuries, with a notable geographical spread in the case studies (from Hungary to Ireland to Poland–Lithuania, among others). Also includes a discussion of the definition of a mercenary in this period. Excellent for wide coverage of the medieval period, but as the book consists of conference proceedings, some pieces are less polished than others.

  • Kiernan, V. G. “Foreign Mercenaries and Absolute Monarchy.” Past & Present 11 (April 1957): 66–86.

    DOI: 10.1093/past/11.1.66

    Kiernan examines the use of foreign fighters in the armies of continental Europe, mainly focusing on the French as employers and examining the wide range of nationalities that were employed as mercenaries. Argues that mercenaries were essential in the transition from feudal states to absolute monarchies. Available online for purchase or by subscription.

  • Mockler, Anthony. The Mercenaries. London: Macdonald, 1969.

    Begins with an analysis of medieval mercenaries and works through all main instances of mercenary use up until the early 1970s. Comprehensive and readable, it was for a long time the only book available on the history of mercenary use; it has been a main starting point for historical investigations into mercenaries. Its scholarly utility is diminished by an absence of referencing or a bibliography, making it impossible to analyze sources.

  • Mockler, Anthony. The New Mercenaries. London: Sidgwick and Jackson, 1985.

    Mockler provides a brief history of mercenary use before focusing on mercenaries in Africa in the postdecolonization period. The book is still the definitive (if not the only) detailed source on this period and full of colorful anecdotes. Again, it suffers from an absence of referencing and documentation.

  • Parrott, David. The Business of War: Military Enterprise and Military Revolution in Early Modern Europe. Cambridge, UK: Cambridge University Press, 2012.

    An excellent survey of how military organization relied on private provision across Europe, particularly useful in its comparative analysis of mercenaries in different countries. Has an unusual focus on the private provision of military support tasks, including the maintenance of armed men but also logistical supply chains, weapons and munitions, and even the building of fortresses.

  • Percy, Sarah. Mercenaries: The History of a Norm in International Relations. Oxford: Oxford University Press, 2007.

    This book takes a long view of mercenary activity from the 12th century to the present use of private security companies. It operates from an explicitly international-relations academic standpoint, considering the question of how norms against mercenary use have influenced state decisions about when and whether to use mercenaries.

  • Singer, Peter W. Corporate Warriors: The Rise of the Privatized Military Industry. 2d ed. Ithaca, NY, and London: Cornell University Press, 2008.

    The first sustained scholarly work on private military companies and private security companies. It contains a historical overview of mercenaries and is a good general introduction to the topic. The second addition adds a chapter to update the analysis to 2008, considering the war in Iraq, but as with any analysis of contemporary events the newer sections become quickly dated.

  • Thomson, Janice E. Mercenaries, Pirates, and Sovereigns: State-Building and Extraterritorial Violence in Early Modern Europe. Princeton, NJ: Princeton University Press, 1994.

    Considers mercenaries alongside privateers and mercantile companies as private actors who wielded force outside state control. It focuses mainly on mercenary activity from the 15th to the 19th centuries and argues that the gradual monopolization of force in the hands of the state in the 19th century was responsible for the disappearance of mercenaries from European armies.

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