Evolution of the Law of Armed Conflict

Edmarverson A. Santos
Jun 25
15 min read

I. Introduction: Defining the Law of Armed Conflict (LOAC)

The evolution of the Law of Armed Conflict reflects humanity’s long-standing effort to impose legal and ethical boundaries on the conduct of war. As a specialized branch of public international law, the Law of Armed Conflict (LOAC)—also known as International Humanitarian Law (IHL)—regulates hostilities by setting clear limits on how wars are fought, with the primary objective of protecting those not participating in combat and restricting the means and methods of warfare.

Historically, warfare was often brutal and unrestricted. Yet, even in antiquity, societies developed customs to mitigate suffering during conflicts. These customs later evolved into codified rules, especially during the 19th and 20th centuries, when the devastating consequences of industrialized warfare prompted urgent legal developments. Today, LOAC encompasses a robust legal framework rooted in both treaty law (such as the Geneva Conventions) and customary international law, with applications in both international and non-international armed conflicts.

The distinction between jus ad bellum and jus in bello is critical. While jus ad bellum governs the legality of resorting to force between states, LOAC falls under jus in bello, applying regardless of who initiated the conflict. This separation reinforces a fundamental principle: once hostilities begin, all parties are bound by the same humanitarian rules, irrespective of their justification for war.

Core principles of LOAC include:

Distinction: Differentiating between combatants and non-combatants.
Proportionality: Avoiding attacks where civilian harm would be excessive in relation to the anticipated military advantage.
Military Necessity: Permitting only those measures required to achieve a legitimate military objective.
Humanity: Prohibiting unnecessary suffering.

LOAC is not static. It has expanded and adapted in response to evolving technologies, new forms of conflict, and emerging humanitarian concerns. The next sections explore how the law developed historically and how it continues to respond to contemporary challenges.

II. Ancient and Religious Foundations

Long before formal treaties and conventions existed, the foundations of the Law of Armed Conflict were evident in ancient customs and religious teachings. These early practices demonstrated a rudimentary recognition of the need to impose moral and behavioral limits during times of war, laying the groundwork for the evolution of the Law of Armed Conflict.

1. Ancient Civilizations and Customary Restraints

Early empires—including those of Mesopotamia, Egypt, Greece, and Rome—followed unwritten norms in warfare. The Code of Hammurabi (c. 1754 BCE) and Hittite treaties provided rules on the treatment of prisoners and oaths of war, reflecting an early concern for regulated conduct. In ancient Greece, truces were respected during the Olympic Games, illustrating the principle of temporary immunity for civilians.

The Roman concept of jus fetiale governed declarations of war and peace, emphasizing formal procedures and the notion that not all wars were justifiable without prior warning—an embryonic form of jus ad bellum.

2. Indian and Chinese Legal Traditions

In South Asia, the Laws of Manu and the Mahabharata offered detailed rules of engagement:

Combatants were to fight only equals.
Civilians, prisoners, and the wounded were not to be harmed.
Poisoned weapons and attacks on the unarmed were forbidden.

Similarly, Chinese philosopher Mozi (5th century BCE) criticized aggressive wars and advocated for defensive restraint, while Confucian ethics stressed the importance of justice and humanity in conflict resolution.

3. Religious Contributions to Humanitarian Conduct in War

Religion	Core Teachings on Warfare
Judaism	The Hebrew Bible includes rules for besieging cities (Deut. 20), requiring offers of peace and protection for non-combatants.
Christianity	Early Christian thought, later developed by theologians like Augustine and Aquinas, introduced just war theory and moral limits on violence.
Islam	The Qur’an and Hadith prohibit harm to non-combatants, destruction of crops, and require humane treatment of prisoners. Caliph Abu Bakr issued ethical commands to soldiers resembling modern IHL.
Buddhism	Although fundamentally pacifist, Buddhist rulers like Ashoka acknowledged military necessity but promoted compassion and non-violence even in conflict.

These doctrines shared overlapping values: restraint, mercy, and responsibility, which became embedded in the moral logic of later humanitarian law.

4. Influence on Customary International Law

Though not formally codified in treaties, these traditions collectively influenced customary international law by:

Establishing a moral duty to protect the weak.
Justifying limits on who can be targeted and how war should be waged.
Laying the moral and philosophical groundwork for future legal codification.

In summary, ancient and religious traditions were instrumental in shaping the ethical contours of armed conflict. They introduced key principles that modern law would later formalize—marking the true beginning of the evolution of the Law of Armed Conflict.

III. From Chivalric Codes to Early State Practice

The medieval and early modern periods marked a transition from unwritten moral codes to more structured frameworks guiding the conduct of warfare. These developments contributed significantly to the evolution of the Law of Armed Conflict, particularly through the emergence of chivalric norms, just war theory, and the first state-driven attempts at codification.

1. Medieval Codes of Chivalry

During the Middle Ages, the European knightly class followed chivalric codes—a mix of military discipline and Christian ethics. While these were not legally binding, they introduced important ideas:

Protection of women, children, and clergy.
Prohibition against attacking unarmed enemies.
The granting of quarter to surrendered combatants.

The Peace and Truce of God movements, supported by the Catholic Church, aimed to limit violence during certain days and protect non-combatants. These religious-political initiatives foreshadowed the humanitarian goals of later legal regimes.

2. Just War Theory: Scholastic Foundations

Medieval theologians refined the philosophical underpinnings of war. Notably:

St. Augustine (4th century) justified war to restore peace and order but emphasized restraint and moral intent.
Thomas Aquinas (13th century) systematized just war theory (bellum iustum), outlining three conditions:
- War must be declared by a legitimate authority.
- It must have a just cause.
- It must be fought with right intention.

These ideas laid the theoretical foundation for distinguishing between the legality (jus ad bellum) and the conduct (jus in bello) of war—an essential division in LOAC.

3. The Rise of State Sovereignty and Early Diplomatic Norms

The Peace of Westphalia (1648) entrenched the sovereignty of states and formalized the role of diplomacy in conflict resolution. As interstate warfare became more professionalized, states began to develop bilateral military codes and manuals, standardizing treatment of prisoners and wounded soldiers.

4. The Lieber Code (1863): First Modern Codification

Commissioned during the American Civil War, General Orders No. 100, known as the Lieber Code, was the first official document to codify laws of war for a national army. Key features included:

Distinction between combatants and civilians.
Ban on torture, assassination, and unnecessary suffering.
Humane treatment of prisoners of war.

The Lieber Code had international influence, particularly on the Brussels Declaration (1874) and Hague Conventions, marking the transition from customary to written law.

5. Influence on International Legal Development

Early Practice	Contribution to LOAC
Chivalric norms	Introduced protection of civilians and honor in war.
Just War doctrine	Grounded legal discussions on causes and conduct.
Lieber Code (1863)	Set precedent for national codification of LOAC.
Brussels Declaration (1874)	Drafted multilateral guidelines on warfare (non-binding but influential).

In this period, the principles of necessity, distinction, and humanity began to shift from moral ideals to legal norms. These developments set the stage for the formalized humanitarian law that would emerge in the 20th century, further advancing the evolution of the Law of Armed Conflict.

IV. Geneva Conventions and the Birth of Modern IHL

The Geneva Conventions represent a decisive milestone in the evolution of the Law of Armed Conflict, marking the transition from moral and military codes to an integrated legal framework designed to protect human dignity in times of war. While earlier efforts laid the philosophical and customary groundwork, the Geneva regime institutionalized the principles of international humanitarian law (IHL) in binding treaties.

1. The 1864 Geneva Convention: A Humanitarian Breakthrough

Driven by the humanitarian advocacy of Henri Dunant, who witnessed the horrors of the Battle of Solferino (1859), the First Geneva Convention was adopted in 1864. It provided:

Legal protection to wounded soldiers on the battlefield.
Neutral status to medical personnel and facilities.
The use of the Red Cross emblem to mark humanitarian assistance.

Though limited in scope, this treaty reflected a foundational shift: wartime suffering was no longer an inevitable consequence but a condition subject to legal restraint.

2. Subsequent Revisions and Expansion (1906, 1929)

Over the following decades, the Geneva Convention was revised to respond to changing wartime realities:

1906 Convention: Broadened protection for wounded combatants and improved medical protocols.
1929 Convention: Introduced detailed provisions on the treatment of prisoners of war, anticipating the need for humane custody.

Despite these advances, World War I exposed serious gaps in the existing legal regime, particularly regarding the protection of civilians.

3. The 1949 Geneva Conventions: A Comprehensive System

The atrocities of World War II, including mass civilian casualties and genocide, led to a complete overhaul of IHL. In 1949, four Geneva Conventions were adopted:

Geneva Convention	Focus
I	Protection of wounded and sick in armed forces on land
II	Protection of wounded, sick, and shipwrecked at sea
III	Treatment of prisoners of war
IV	Protection of civilian persons in time of war

Each convention emphasized common humanitarian principles:

Prohibition of torture, inhumane treatment, and collective punishment.
Obligation to care for the wounded and sick, without discrimination.
Rights to fair trial and communication for detainees.

Importantly, Common Article 3 extended protections to non-international armed conflicts—civil wars, rebellions, and internal strife—thus closing a critical legal gap.

4. Key Legal Innovations

The 1949 framework advanced the evolution of the Law of Armed Conflict by introducing:

Legal obligations regardless of reciprocity: States must uphold IHL even if the adversary violates it.
Individual criminal responsibility for grave breaches (e.g., torture, killing of protected persons).
Universal jurisdiction: States can prosecute war crimes regardless of where they occur or the nationality of the accused.

5. Impact and Global Acceptance

The Geneva Conventions have achieved near-universal ratification—194 States are parties—making them the most widely accepted international treaties. They serve as the legal bedrock of IHL and are complemented by:

The 1977 Additional Protocols, which expanded protections to civilian populations and guerrilla fighters.
Jurisprudence from international courts (e.g., ICTY, ICC) reinforcing their interpretation and enforcement.

The Geneva Conventions transformed the humanitarian ideals of the past into enforceable obligations. They remain central to the evolution of the Law of Armed Conflict, forming the core of modern legal protections in warfare.

V. The Hague Regulations and Legal Formalization

While the Geneva Conventions focus on the protection of persons during conflict, the Hague Regulations address the conduct of hostilities, particularly the means and methods of warfare. Together, they form the twin pillars of modern International Humanitarian Law (IHL). The Hague Conventions of 1899 and 1907 represent a crucial stage in the evolution of the Law of Armed Conflict by initiating formal multilateral agreements that regulated how wars are fought.

1. Origins and Diplomatic Context

The First Hague Peace Conference (1899) was convened by Tsar Nicholas II of Russia to promote arms control and peaceful conflict resolution. Though disarmament efforts failed, the conference produced:

The Convention (II) with Respect to the Laws and Customs of War on Land.
The Regulations annexed to the Convention, which detailed rules on military conduct, treatment of prisoners, and occupation.

The Second Hague Conference (1907) expanded these norms with 13 new conventions, including regulations on naval warfare and the rights of neutral powers.

2. Key Legal Contributions of the Hague Regulations

The Hague Regulations were the first binding multilateral treaties to:

Define legitimate combatants and irregular fighters.
Prohibit certain weapons and tactics (e.g., poison, killing or wounding enemies who surrender).
Codify protections for civilians in occupied territories.
Ban pillage and unnecessary destruction of property.

Selected Prohibitions Under the Hague Regulations:

Prohibited Action	Legal Basis (1907 Hague Regulation)
Poison and poisoned weapons	Article 23(a)
Killing or wounding enemies who surrender	Article 23(c)
Attacking undefended towns and villages	Article 25
Destruction or seizure of enemy property without necessity	Article 23(g)

These rules sought to humanize war by requiring that violence be constrained by legal norms and military necessity.

3. Legal Status and Customary Law

Although not all states ratified the Hague Conventions, many of their provisions—especially the Hague Regulations on land warfare—are considered customary international law, meaning they are binding on all states regardless of treaty status.

This was confirmed in the Nuremberg Trials and subsequent international jurisprudence, which treated violations of Hague law as war crimes.

4. Complementarity with Geneva Law

The Hague and Geneva systems complement one another:

Hague Law regulates how wars are fought (methods and means).
Geneva Law regulates who is protected during war (victims and non-combatants).

This dual structure has been reinforced by later treaties, including the 1977 Additional Protocols, which integrate both dimensions into a unified legal framework.

5. Enduring Influence on Modern Conflict Law

Despite being over a century old, the Hague Regulations still inform:

Military manuals and rules of engagement.
International court rulings on unlawful attacks, occupation conduct, and targeting decisions.
Legal education for officers and humanitarian workers.

They also provided the foundation for future arms control agreements (e.g., Chemical Weapons Convention, 1993) and inspired key principles like distinction, proportionality, and unnecessary suffering, all central to the evolution of the Law of Armed Conflict.

The Hague Regulations were instrumental in shifting warfare from being governed by ad hoc customs to being subject to formal, written legal norms. By codifying battlefield conduct, they created a structured legal environment that continues to shape humanitarian protections in armed conflict today.

VI. Contemporary Developments and Protocols

In response to the shifting nature of warfare, the international community has built upon the Geneva and Hague traditions through contemporary legal developments and protocols that address the realities of modern armed conflicts. These instruments have expanded protections, clarified legal definitions, and adapted existing frameworks to new threats. This progressive expansion is a defining feature in the evolution of the Law of Armed Conflict.

1. The 1977 Additional Protocols: A Critical Turning Point

The Additional Protocols I and II to the Geneva Conventions, adopted in 1977, were landmark achievements in humanitarian law.

Protocol I – International Armed Conflicts

Reinforced the principle of distinction between civilians and combatants (Art. 48–51).
Expanded the scope of protection for civilian populations, including in occupied territories.
Addressed guerrilla warfare by recognizing fighters in wars of national liberation as lawful combatants (Art. 1(4), Art. 44).

Protocol II – Non-International Armed Conflicts

First treaty to specifically regulate internal conflicts, which had previously relied solely on Common Article 3.
Enhanced protections for civilians, detainees, and wounded in civil wars, insurgencies, and internal disturbances.
Prohibited acts like collective punishment, terrorism, and hostage-taking.

Despite some states (e.g., the United States) not ratifying the protocols, many of their provisions are now considered customary international law.

2. Customary Law and the Role of International Jurisprudence

In situations where treaties do not apply, customary international humanitarian law (CIHL) fills the gap. The International Committee of the Red Cross (ICRC) identified 161 rules of CIHL in its 2005 study, which are binding regardless of treaty ratification.

International courts have also played a key role:

ICTY (e.g., Tadić case) clarified the applicability of IHL in non-international conflicts and helped define direct participation in hostilities.
ICC (Rome Statute, 1998) codified war crimes, including attacks on civilians, sexual violence in conflict, and use of prohibited weapons.

3. Legal Responses to Technological Warfare

Modern conflicts increasingly involve new technologies that test the limits of existing IHL:

Technology	Legal Challenge	Current Response
Drones (UAVs)	Targeted killings, distinction, accountability	Customary principles applied; debate on transparency and oversight
Cyber Warfare	Attribution of attacks, civilian-military boundaries	Tallinn Manual (non-binding); IHL principles adapted by analogy
Autonomous Weapons	Lack of human control, predictability	UN debates ongoing; ICRC urges preemptive legal regulation

The Martens Clause, a general clause included in Protocol I, ensures that humanitarian principles continue to apply in cases where new means or methods of warfare are not explicitly regulated.

4. Expanding Protections for Vulnerable Groups

Recent years have seen a growing focus on groups particularly affected by war:

Women and girls: Addressing gender-based violence through UNSC Resolution 1325 and ICC jurisprudence.
Children: The Optional Protocol on the Involvement of Children in Armed Conflict (2000) prohibits child soldier recruitment.
Refugees and Internally Displaced Persons (IDPs): IHL now intersects more directly with international human rights and refugee law.

5. Compliance and Implementation Mechanisms

Effective enforcement of IHL remains a challenge. Several mechanisms have been strengthened:

Fact-finding commissions (e.g., International Humanitarian Fact-Finding Commission).
National legislation implementing IHL and prosecuting war crimes.
UN bodies and Security Council interventions in cases of mass atrocities.

The ICRC continues to play a vital role in dissemination, training, and confidential diplomacy to ensure compliance.

Contemporary developments have significantly enhanced the scope, clarity, and applicability of international humanitarian law. Through new protocols, legal innovations, and adaptive interpretations, the international community has fortified the humanitarian protections that define the evolution of the Law of Armed Conflict in the 21st century.

VII. Challenges in Modern Conflicts

Despite a comprehensive legal framework established by the Geneva Conventions, the Hague Regulations, and subsequent protocols, modern armed conflicts present complex challenges that test the limits of existing international humanitarian law (IHL).

These challenges reflect the changing nature of warfare—characterized by non-state actors, urban battlefields, and emerging technologies—necessitating continuous interpretation and, at times, reform. These tensions are central to understanding the ongoing evolution of the Law of Armed Conflict.

1. Asymmetric Warfare and Non-State Actors

Contemporary conflicts often involve non-state armed groups operating outside traditional military hierarchies.

Key Issues:

Combatant status: Non-state fighters rarely wear uniforms or carry arms openly, making it difficult to distinguish them from civilians.
Accountability gaps: Non-state actors may not be parties to treaties like the Geneva Conventions, complicating enforcement.
Hostage-taking and civilian targeting: Common tactics violate IHL principles but are difficult to prevent in fragmented warfare environments.

The Tadić case (ICTY, 1995) and Additional Protocol II addressed some of these concerns, but the practical enforcement remains inconsistent.

2. Urban Warfare and Civilian Protection

Armed conflicts increasingly take place in densely populated urban areas—Aleppo, Mosul, Gaza—where combatants are embedded within civilian infrastructure.

Key Legal Challenges:

Application of the principle of distinction is hindered by proximity of civilians to military targets.
Ensuring proportionality becomes more complex as collateral damage increases.
The use of human shields, often by non-state groups, violates IHL but complicates lawful targeting for state forces.

Civilian Impact in Urban Conflicts (Selected Data)

Conflict	Civilian Casualty Rate	Primary Legal Concern
Syria (2011–)	Estimated 50–60%	Use of barrel bombs, chemical weapons
Gaza (2021)	Over 40%	Indiscriminate shelling claims
Mosul (2016–2017)	Approx. 33%	Airstrikes on civilian structures

Source: UN OHCHR, ICRC reports

3. Use of New and Emerging Technologies

a. Drones and Remote Warfare

Raise issues around targeted killings, due process, and civilian casualties.
Complicate attribution of responsibility and legal oversight.
Often used in extraterritorial operations, blurring the boundary between armed conflict and law enforcement.

b. Cyber Operations

Can disrupt hospitals, power grids, or infrastructure, potentially violating IHL if resulting in civilian harm.
Attribution remains difficult, and existing treaties do not explicitly cover cyberattacks.
The Tallinn Manual provides non-binding guidance based on IHL principles.

c. Autonomous Weapons Systems (AWS)

Pose critical questions: Who is accountable if a robot commits a war crime?
The lack of human judgment in AWS use may conflict with IHL requirements of proportionality and precaution.
States and civil society continue to debate bans or strict regulation frameworks.

4. Enforcement and Accountability Deficits

Even with established norms, impunity persists.

Problems:

Limited reach of international courts like the ICC.
Weak national implementation of war crime statutes.
Political resistance to investigations, especially involving powerful states.

Enforcement depends heavily on state cooperation, civil society advocacy, and public transparency—often lacking in active conflict zones.

5. Climate Change and Resource Conflicts

Environmental degradation, droughts, and resource scarcity increasingly contribute to armed conflict, yet IHL offers limited tools for prevention.

Attacks on infrastructure like water systems and crops can violate IHL when used to starve civilian populations (Protocol I, Art. 54).
The protection of the environment during warfare is addressed only partially (e.g., ENMOD Convention 1976), leaving legal gaps.

The modern battlefield is fluid, fragmented, and technologically advanced. While the core principles of IHL—distinction, proportionality, necessity, and humanity—remain relevant, their application is under constant strain. These challenges highlight the urgent need for legal clarity, operational training, and political will to uphold the values central to the evolution of the Law of Armed Conflict.

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VIII. Conclusion: Continuity and Future of LOAC

The evolution of the Law of Armed Conflict has followed a centuries-long trajectory from unwritten customs and religious teachings to a sophisticated legal regime codified in binding treaties and reinforced by international jurisprudence. From the Geneva Conventions’ humanitarian mandates to the Hague Regulations’ constraints on military conduct, the foundations of International Humanitarian Law (IHL) have consistently aimed to mitigate human suffering in times of war.

Despite this progress, armed conflict remains a dynamic and often unpredictable reality. The legal frameworks developed throughout the 20th century—especially the 1949 Geneva Conventions and the 1977 Additional Protocols—continue to serve as the core of IHL. Yet they face mounting challenges from the complexities of asymmetric warfare, technological innovation, cyber operations, and the growing involvement of non-state actors. These developments stress the necessity of adaptability and renewed commitment to humanitarian norms.

The resilience of LOAC lies in its underlying principles: distinction, proportionality, military necessity, and humanity. These principles remain applicable in both conventional and unconventional warfare, providing ethical and legal boundaries that reflect the international community’s shared values. However, their relevance depends on rigorous implementation, updated legal interpretations, and political will.

Going forward, several imperatives are clear:

Strengthening national legal frameworks for war crimes accountability.
Enhancing international cooperation in the regulation of emerging technologies in warfare.
Expanding training and dissemination of LOAC among armed forces, non-state actors, and civil society.
Supporting institutions like the ICRC, ICC, and regional bodies in monitoring compliance.

The continuity of the Law of Armed Conflict is not guaranteed by treaties alone. It depends on vigilance, enforcement, and collective moral responsibility. As warfare evolves, so too must the legal structures that seek to humanize it. The future of LOAC will rest on our ability to apply old principles to new contexts—ensuring that humanitarian law remains a living, enforceable, and universally respected body of international law.

Reference

Kolb, R., & Hyde, R. (2008). An Introduction to the International Law of Armed Conflicts. Hart Publishing.
Geneva Conventions I–IV (1949) and Additional Protocols I & II (1977).
Hague Conventions and Regulations (1899, 1907).
Lieber Code (General Orders No. 100), U.S. War Department (1863).
International Committee of the Red Cross (ICRC), Customary International Humanitarian Law, Vol. I–II (2005).
Prosecutor v. Tadić, ICTY, Case No. IT-94-1 (1995 & 1999).
Military and Paramilitary Activities in and against Nicaragua (Nicaragua v. United States), ICJ Reports (1986).
Legality of the Threat or Use of Nuclear Weapons, ICJ Advisory Opinion (1996).
Tallinn Manual on the International Law Applicable to Cyber Warfare (2013).
UN Optional Protocol on the Involvement of Children in Armed Conflict (2000).