International humanitarian law (IHL) sets rules for armed conflicts, protecting civilians and combatants. It's based on key principles like distinction, proportionality, and humanity. IHL applies to all parties in conflicts, regulating warfare methods and establishing enforcement mechanisms.

IHL has ancient roots but was formalized in the 19th century. The Geneva Conventions of 1949 and Additional Protocols of 1977 are its core. IHL continues to evolve, addressing new challenges like cyber warfare and autonomous weapons.

International Humanitarian Law

Core Principles and Definition

• International humanitarian law (IHL) limits effects of armed conflict on civilians and combatants for humanitarian reasons
• Principle of distinction requires parties to differentiate between civilians and combatants (military uniforms, clearly marked facilities)
• Proportionality prohibits excessive civilian casualties relative to military advantage (avoiding bombing densely populated areas)
• Military necessity permits only actions for legitimate military purposes (destroying enemy weapons cache)
• Humanity forbids unnecessary suffering or destruction (banning certain weapons like chemical agents)
• Precaution requires measures to minimize civilian casualties (advance warnings of attacks)

Application and Scope

• Applies to all parties in armed conflicts regardless of who initiated hostilities
• Covers protection of persons not participating in hostilities (medical personnel, aid workers)
• Regulates means and methods of warfare (prohibiting certain weapons, tactics)
• Establishes mechanisms for implementation and enforcement (war crimes tribunals)
• Interacts with other bodies of law (human rights law, international criminal law)

History of International Humanitarian Law

Ancient and Early Modern Foundations

• Roots in ancient civilizations and religions regulated warfare (Greek city-states, Islamic rules of war)
• 19th century saw establishment of International Committee of the Red Cross in 1863
• First Geneva Convention of 1864 focused on protecting wounded soldiers on battlefield
• Hague Conventions of 1899 and 1907 developed rules on conduct of hostilities (aerial bombardment, naval warfare)

Modern Development and Codification

• Four Geneva Conventions of 1949 expanded protection for wounded, prisoners, civilians
• Additional Protocols of 1977 addressed international and non-international conflicts
• Recent developments ban specific weapons (landmines, cluster munitions)
• New challenges addressed include cyber warfare and autonomous weapon systems
• International criminal tribunals further developed IHL through case law (ICTY, ICC)

Sources of International Humanitarian Law

Primary Treaty Sources

• Geneva Conventions of 1949 and Additional Protocols form core of IHL
• Hague Conventions of 1899 and 1907 regulate means and methods of warfare
• Specific weapons treaties prohibit or restrict use (Chemical Weapons Convention)
• Rome Statute of the International Criminal Court defines war crimes

Customary Law and Other Sources

• Customary IHL derived from consistent state practice and opinio juris
• Judicial decisions from international courts interpret and develop IHL (ICJ, ICTY)
• Military manuals and official state statements evidence customary law
• Soft law instruments influence development (UN resolutions, ICRC guidelines)
• Academic writings and expert opinions contribute to interpretation

International vs Non-International Armed Conflicts

Defining Characteristics

• International armed conflicts (IACs) occur between states
• Non-international armed conflicts (NIACs) involve at least one non-state armed group
• IAC threshold low, any use of armed force between states sufficient
• NIAC requires higher threshold of violence and organization of non-state group
• Occupation rules apply only in IACs (Israel's occupation of West Bank)

Applicable Law and Status of Parties

• Full body of IHL applies to IACs, limited set for NIACs
• Common Article 3 of Geneva Conventions and Additional Protocol II primary NIAC sources
• Equality of belligerents in IACs grants equal rights and obligations
• Legal status of non-state armed groups in NIACs remains controversial
• Combatant status and POW protections exist in IACs but not NIACs
• Detained fighters in NIACs subject to domestic criminal law