Week 1
Weapons and the Laws of Armed Conflict
Chapter 1 - Introduction
1.1 The Emergence of Weapons Law
Early warfare and absence of regulation
In the earliest forms of warfare, there was little or no recognition of legal or normative limits
on weapons. Military advantage prevailed, and actors freely exploited superior weapons,
regardless of the suffering inflicted. The idea that weapons should be regulated did not
initially exist.
The rationale for regulating weapons rather than banning war
Although it may appear counterintuitive to regulate tools of killing rather than prohibit war
itself, international law adopts a pragmatic approach. War is treated as a factual reality, and
the law focuses on mitigating its worst effects rather than eliminating it altogether. Weapons
law therefore seeks to ensure that even in combat, internationally accepted norms are
respected.
Morality and treaty-making
Weapons law treaties were not always driven by shared moral imperatives. States often
negotiated such treaties based on national interests, strategic concerns, and differing moral
perspectives. Moral considerations may have influenced outcomes, but they were not
necessarily the primary motivation.
Customary law development
Over time, repeated practices in warfare evolved into customary international law. These
customs imposed obligations on States, prohibited certain methods of warfare, and limited
who and what could be lawfully attacked. Weapons law thus developed alongside broader
rules governing the conduct of hostilities.
1.2 Weapons Law in Context
Weapons law within the law of armed conflict
Weapons law forms part of the wider law of armed conflict (LOAC), which regulates military
operations, protects victims of war, safeguards cultural property, and establishes
accountability mechanisms such as international criminal courts.
Hague law and Geneva law
Historically, the law of armed conflict developed along two tracks:
● Hague law, regulating weapons and methods of warfare;
● Geneva law, protecting victims of armed conflict.
The 1977 Additional Protocols significantly bridged this divide, making the distinction
largely historical rather than practical.
,International vs non-international armed conflict
A further distinction exists between rules applicable in international armed conflicts and
those applicable in non-international armed conflicts. Although these regimes have
converged over time, differences remain in weapons law. These issues are addressed later in
the book.
Relationship with arms control law
Some weapons law rules are better understood as arms control or disarmament measures,
focusing on production, stockpiling, transfer, or deployment rather than battlefield conduct.
Certain treaties (e.g. Chemical Weapons Convention, Biological Weapons Convention,
Ottawa Convention) are hybrid instruments and are included because they directly affect
lawful use in armed conflict.
Core function of weapons law
Weapons law prohibits certain weapons outright and restricts the use of others. Weapons not
prohibited may be lawfully used, provided that targeting and conduct-of-hostilities rules are
respected.
1.3 Jus ad Bellum and Jus in Bello
Conceptual distinction
A clear separation must be maintained between:
● Jus ad bellum (law governing the use of force), and
● Jus in bello (law governing conduct during armed conflict).
Legal equality of belligerents (= strijdende partijen)
Once an armed conflict exists, all parties are equally bound by, and entitled to the protections
of, the law of armed conflict. The legality or illegality of resorting to force does not affect the
applicability of jus in bello rules.
Relevance to the book
Because weapons law operates within jus in bello, questions of jus ad bellum are largely
irrelevant to the subject matter of this book.
1.4 Meaning of Weapon, Means, and Methods of Warfare
Weapon
A weapon is an object or system designed to apply offensive force against an enemy or
military objective, typically causing injury, death, or damage.
Means of warfare
The “means of warfare” include weapons themselves, weapons platforms, and associated
equipment used to deliver force during hostilities.
Methods of warfare
“Methods of warfare” refer to how force is used, including general operational categories
(e.g. bombardment, blockade) and specific tactics (e.g. siege, high-altitude bombing).
,1.5 Outline of the Text
Purpose of the early chapters
The initial chapters explain the evolution, components, and legal context of weapons law.
This background is necessary to understand the regulation of specific weapons.
Scope of weapons law
Weapons law addresses:
● Whether a weapon is lawful per se;
● Whether a specific intended use complies with applicable rules.
Targeting decisions themselves fall outside weapons law, even though the distinction may
sometimes seem artificial.
1.7 Arms Trade Treaty
Nature of the Arms Trade Treaty (ATT)
The ATT, adopted in 2013 and in force since 2014, primarily regulates the international trade
in conventional arms. It is not a law of armed conflict treaty, though it has humanitarian
objectives.
Scope and obligations
The treaty applies to major conventional weapons, small arms, light weapons, ammunition,
and parts. States must establish national control systems and export control lists.
Prohibitions and risk assessment
Transfers are prohibited if they would violate UN Charter obligations or if the exporting State
knows the arms would be used to commit serious international crimes. In other cases, States
must assess risks before authorizing exports.
Relevance to weapons law
Although outside the core scope of weapons law, the ATT is briefly discussed due to its
indirect impact on armed conflict and weapons regulation.
Chapter 2 - The Evolution of the Law of Weaponry
2.1 Introduction
This chapter provides a selective, high-level account of how the law of weaponry emerged. It
does not aim to reconstruct negotiating histories or State positions, but instead highlights key
milestones that shaped the body of law. The approach reflects the book’s broader
methodology: interpreting weapons law primarily through the ordinary meaning of legal
texts, rather than travaux préparatoires (= preparatory works).
2.2 The Earliest Rules
Early restrictions on weapons can be found in ancient sources such as the Hindu Code of
Manu, Greek customs prohibiting “unhoplite” arms, and medieval ecclesiastical attempts to
ban crossbows. While these examples show early ethical constraints, they do not constitute
a coherent international law of weaponry.
Nevertheless, there was widespread early acceptance that certain practices, most notably the
use of poison, were improper. The modern law of weaponry thus has roots in pre-existing
customs, which nineteenth-century jurists later recognized as binding law.
, 2.3 Lieber Code (1863)
The Lieber Code, drafted during the American Civil War, was the first comprehensive
codification of the laws of land warfare. It introduced a structured concept of military
necessity, while explicitly limiting it. Lieber rejected cruelty, defining it as suffering inflicted
for its own sake or for revenge, and explicitly prohibited poison. This marks an early
formulation of what later became the principle of superfluous injury and unnecessary
suffering, though still framed narrowly as suffering without purpose.
2.4 St Petersburg Declaration 1868
The St Petersburg Declaration represents a foundational moment in weapons law. Its
preamble articulated enduring principles:
● War’s only legitimate aim is to weaken enemy military forces;
● Disabling combatants is sufficient;
● Weapons that unnecessarily aggravate suffering or render death inevitable are
unlawful.
This established the link between military necessity, humanity, and unnecessary suffering,
framing them as principles capable of supporting concrete prohibitions. Although initially
limited to wars between “civilized nations,” the Declaration is best understood as the first
step toward general rules of application.
2.5 Brussels Declaration 1874 and Oxford Manual 1880
Neither instrument was a binding treaty, but both significantly clarified and consolidated
emerging rules. The Brussels Declaration stated explicitly that belligerents do not have
unlimited freedom in choosing means of injuring the enemy and prohibited poison and
weapons causing unnecessary suffering.
The Oxford Manual reaffirmed these principles, stressing abstention from needless severity
and prohibiting poison and weapons that aggravate wounds. Together, these texts reinforced
the normative core of weapons law prior to formal treaty codification.
2.6 Hague Peace Conference 1899
By 1899, specific prohibitions were few, but general principles were well developed. The
Hague Conferences sought to address new technologies through treaty law. Early treaties
contained general participation clauses, limiting their applicability to conflicts exclusively
between contracting States. This reflected the consensual nature of treaty obligations at the
time, even if it appears inconsistent with the humanitarian ideals expressed in their
preambles. The 1899 Declarations on asphyxiating gases and expanding bullets were
especially significant, though they proved insufficient to prevent later abuses.
2.7 Hague Peace Conference 1907 and the Martens Clause
The 1907 Hague Regulations are widely regarded as declaratory of customary international
law. Articles 22 and 23 codified two enduring principles:
● the right to choose means of warfare is not unlimited;
● weapons causing unnecessary suffering and poison are prohibited.
Weapons and the Laws of Armed Conflict
Chapter 1 - Introduction
1.1 The Emergence of Weapons Law
Early warfare and absence of regulation
In the earliest forms of warfare, there was little or no recognition of legal or normative limits
on weapons. Military advantage prevailed, and actors freely exploited superior weapons,
regardless of the suffering inflicted. The idea that weapons should be regulated did not
initially exist.
The rationale for regulating weapons rather than banning war
Although it may appear counterintuitive to regulate tools of killing rather than prohibit war
itself, international law adopts a pragmatic approach. War is treated as a factual reality, and
the law focuses on mitigating its worst effects rather than eliminating it altogether. Weapons
law therefore seeks to ensure that even in combat, internationally accepted norms are
respected.
Morality and treaty-making
Weapons law treaties were not always driven by shared moral imperatives. States often
negotiated such treaties based on national interests, strategic concerns, and differing moral
perspectives. Moral considerations may have influenced outcomes, but they were not
necessarily the primary motivation.
Customary law development
Over time, repeated practices in warfare evolved into customary international law. These
customs imposed obligations on States, prohibited certain methods of warfare, and limited
who and what could be lawfully attacked. Weapons law thus developed alongside broader
rules governing the conduct of hostilities.
1.2 Weapons Law in Context
Weapons law within the law of armed conflict
Weapons law forms part of the wider law of armed conflict (LOAC), which regulates military
operations, protects victims of war, safeguards cultural property, and establishes
accountability mechanisms such as international criminal courts.
Hague law and Geneva law
Historically, the law of armed conflict developed along two tracks:
● Hague law, regulating weapons and methods of warfare;
● Geneva law, protecting victims of armed conflict.
The 1977 Additional Protocols significantly bridged this divide, making the distinction
largely historical rather than practical.
,International vs non-international armed conflict
A further distinction exists between rules applicable in international armed conflicts and
those applicable in non-international armed conflicts. Although these regimes have
converged over time, differences remain in weapons law. These issues are addressed later in
the book.
Relationship with arms control law
Some weapons law rules are better understood as arms control or disarmament measures,
focusing on production, stockpiling, transfer, or deployment rather than battlefield conduct.
Certain treaties (e.g. Chemical Weapons Convention, Biological Weapons Convention,
Ottawa Convention) are hybrid instruments and are included because they directly affect
lawful use in armed conflict.
Core function of weapons law
Weapons law prohibits certain weapons outright and restricts the use of others. Weapons not
prohibited may be lawfully used, provided that targeting and conduct-of-hostilities rules are
respected.
1.3 Jus ad Bellum and Jus in Bello
Conceptual distinction
A clear separation must be maintained between:
● Jus ad bellum (law governing the use of force), and
● Jus in bello (law governing conduct during armed conflict).
Legal equality of belligerents (= strijdende partijen)
Once an armed conflict exists, all parties are equally bound by, and entitled to the protections
of, the law of armed conflict. The legality or illegality of resorting to force does not affect the
applicability of jus in bello rules.
Relevance to the book
Because weapons law operates within jus in bello, questions of jus ad bellum are largely
irrelevant to the subject matter of this book.
1.4 Meaning of Weapon, Means, and Methods of Warfare
Weapon
A weapon is an object or system designed to apply offensive force against an enemy or
military objective, typically causing injury, death, or damage.
Means of warfare
The “means of warfare” include weapons themselves, weapons platforms, and associated
equipment used to deliver force during hostilities.
Methods of warfare
“Methods of warfare” refer to how force is used, including general operational categories
(e.g. bombardment, blockade) and specific tactics (e.g. siege, high-altitude bombing).
,1.5 Outline of the Text
Purpose of the early chapters
The initial chapters explain the evolution, components, and legal context of weapons law.
This background is necessary to understand the regulation of specific weapons.
Scope of weapons law
Weapons law addresses:
● Whether a weapon is lawful per se;
● Whether a specific intended use complies with applicable rules.
Targeting decisions themselves fall outside weapons law, even though the distinction may
sometimes seem artificial.
1.7 Arms Trade Treaty
Nature of the Arms Trade Treaty (ATT)
The ATT, adopted in 2013 and in force since 2014, primarily regulates the international trade
in conventional arms. It is not a law of armed conflict treaty, though it has humanitarian
objectives.
Scope and obligations
The treaty applies to major conventional weapons, small arms, light weapons, ammunition,
and parts. States must establish national control systems and export control lists.
Prohibitions and risk assessment
Transfers are prohibited if they would violate UN Charter obligations or if the exporting State
knows the arms would be used to commit serious international crimes. In other cases, States
must assess risks before authorizing exports.
Relevance to weapons law
Although outside the core scope of weapons law, the ATT is briefly discussed due to its
indirect impact on armed conflict and weapons regulation.
Chapter 2 - The Evolution of the Law of Weaponry
2.1 Introduction
This chapter provides a selective, high-level account of how the law of weaponry emerged. It
does not aim to reconstruct negotiating histories or State positions, but instead highlights key
milestones that shaped the body of law. The approach reflects the book’s broader
methodology: interpreting weapons law primarily through the ordinary meaning of legal
texts, rather than travaux préparatoires (= preparatory works).
2.2 The Earliest Rules
Early restrictions on weapons can be found in ancient sources such as the Hindu Code of
Manu, Greek customs prohibiting “unhoplite” arms, and medieval ecclesiastical attempts to
ban crossbows. While these examples show early ethical constraints, they do not constitute
a coherent international law of weaponry.
Nevertheless, there was widespread early acceptance that certain practices, most notably the
use of poison, were improper. The modern law of weaponry thus has roots in pre-existing
customs, which nineteenth-century jurists later recognized as binding law.
, 2.3 Lieber Code (1863)
The Lieber Code, drafted during the American Civil War, was the first comprehensive
codification of the laws of land warfare. It introduced a structured concept of military
necessity, while explicitly limiting it. Lieber rejected cruelty, defining it as suffering inflicted
for its own sake or for revenge, and explicitly prohibited poison. This marks an early
formulation of what later became the principle of superfluous injury and unnecessary
suffering, though still framed narrowly as suffering without purpose.
2.4 St Petersburg Declaration 1868
The St Petersburg Declaration represents a foundational moment in weapons law. Its
preamble articulated enduring principles:
● War’s only legitimate aim is to weaken enemy military forces;
● Disabling combatants is sufficient;
● Weapons that unnecessarily aggravate suffering or render death inevitable are
unlawful.
This established the link between military necessity, humanity, and unnecessary suffering,
framing them as principles capable of supporting concrete prohibitions. Although initially
limited to wars between “civilized nations,” the Declaration is best understood as the first
step toward general rules of application.
2.5 Brussels Declaration 1874 and Oxford Manual 1880
Neither instrument was a binding treaty, but both significantly clarified and consolidated
emerging rules. The Brussels Declaration stated explicitly that belligerents do not have
unlimited freedom in choosing means of injuring the enemy and prohibited poison and
weapons causing unnecessary suffering.
The Oxford Manual reaffirmed these principles, stressing abstention from needless severity
and prohibiting poison and weapons that aggravate wounds. Together, these texts reinforced
the normative core of weapons law prior to formal treaty codification.
2.6 Hague Peace Conference 1899
By 1899, specific prohibitions were few, but general principles were well developed. The
Hague Conferences sought to address new technologies through treaty law. Early treaties
contained general participation clauses, limiting their applicability to conflicts exclusively
between contracting States. This reflected the consensual nature of treaty obligations at the
time, even if it appears inconsistent with the humanitarian ideals expressed in their
preambles. The 1899 Declarations on asphyxiating gases and expanding bullets were
especially significant, though they proved insufficient to prevent later abuses.
2.7 Hague Peace Conference 1907 and the Martens Clause
The 1907 Hague Regulations are widely regarded as declaratory of customary international
law. Articles 22 and 23 codified two enduring principles:
● the right to choose means of warfare is not unlimited;
● weapons causing unnecessary suffering and poison are prohibited.
