Term and Definition of War of Aggression
Ein War of aggression is a military conflict that begins with an act of military aggression by one state against another that is unlawful under international law and not justified. The term plays a central role in both international law and national criminal law systems. A war of aggression fundamentally differs from other forms of military use of force, as, by definition, it violates the prohibition of force under international law as well as specific national laws.
Historical development of the prohibition of war of aggression
International law foundations
The condemnation of the war of aggression as a tool of politics was enshrined in several international treaties and regulations in the 20th century:
- League of Nations Covenant (1919): For the first time, it set out certain procedural rules for the peaceful settlement of disputes, but did not explicitly prohibit wars of aggression.
- Kellogg-Briand Pact (1928): With the so-called ‘Pact of Paris’ it was, for the first time, internationally binding to prohibit war as an instrument of policy.
- Charter of the United Nations (1945): The UN Charter, in Article 2(4), establishes the prohibition of the threat or use of force against the territorial integrity or political independence of any state, which constitutes the general prohibition of wars of aggression.
Development in German law
In Germany, the prohibition of the war of aggression was integrated into the Basic Law and the Criminal Code after World War II, in particular as a response to the Nuremberg Trials, where the ‘crime against peace’ (planning and waging a war of aggression) was prosecuted for the first time.
Legal characteristics and definitions
Definition under international law according to the UN Charter
According to the Charter of the United Nations, any armed attack not covered by grounds of self-defense or Security Council mandate is a war of aggression in violation of international law. The requirements are use of armed force, which no justification (e.g., self-defense) exists, and the violation of the sovereignty of another state.
Exceptions to the prohibition of force
- Self-defense: Article 51 of the UN Charter grants every state the right to individual or collective self-defense if attacked.
- Security Council mandate: Military measures on the basis of a mandate from the UN Security Council are permissible under international law.
German Criminal Law: § 80 Criminal Code (until 2017)
Until the reform of the German Criminal Code in 2017, war of aggression was expressly regulated as a criminal offense under § 80 StGB. It criminalized the preparation or waging of a war of aggression. With the entry into force of the International Criminal Code (VStGB) the offense was specified and adapted to international standards.
International Criminal Code (VStGB)
According to § 13 VStGB, participation in the planning, preparation, initiation or conduct of a war of aggression—in the wording ‘crime of aggression’—is punishable. This applies to the highest political and military leaders who are in a position to control or direct the actions of a state.
The crime of aggression in international criminal law
International Criminal Court (ICC)
The International Criminal Court in The Hague deals with the crime of aggression as one of the core crimes under international criminal law (Art. 8bis of the Rome Statute of the ICC). The requirements include:
- Act of a leader of a state exercising control over the political or military direction,
- Planning, preparation, initiation or execution of an act of aggression,
- the act must constitute a manifest violation of the Charter of the United Nations.
Definition of Aggression (UN General Assembly Resolution 3314)
UN General Assembly Resolution 3314 of 1974 defines the term aggression with a list of specific acts such as invasion, bombardment, blockade, or occupation of foreign territory.
Criminal liability and sanctions
National criminal liability (Germany)
Under the German legal system, the planning, preparation, or conduct of a war of aggression by decision-makers is a criminal offense under the International Criminal Code. The penalties range from multi-year prison sentences to life imprisonment.
International prosecution
At the International Criminal Court, individuals can be held accountable regardless of their nationality, provided the crime is subject to jurisdiction under the Rome Statute and the act was committed after July 1, 2002. Limitations exist, especially regarding the requirement of a UN Security Council resolution for states that have not ratified the Statute.
Legal-doctrinal distinctions
Distinction: War of aggression – defensive case
A key doctrinal difference exists between a war of aggression and a military engagement in self-defense. War of aggression is always unlawful under international law and criminal, whereas a defensive war is permitted under Article 51 of the UN Charter.
Distinction from other criminal offenses
Further distinctions must be made with war crimes, crimes against humanity, and genocide. While these offenses often occur in connection with armed conflict, the crime of aggression addresses the unjustified initiation of a military conflict.
War of aggression in case law and practice
Nuremberg Trials
The prosecution of the leadership of the Third Reich at the Nuremberg Trials set a precedent for individual criminal responsibility for international crimes such as war of aggression.
Current international practice
Since the establishment of the International Criminal Court, practical prosecution of the crime of aggression remains limited, especially due to political circumstances and the need for broad international cooperation.
Literature and further references
- Rome Statute of the International Criminal Court
- UN Charter and Resolution 3314 of the UN General Assembly
- International Criminal Code (VStGB)
- BeckOK StGB, § 13 VStGB
- Fischer, Criminal Code and Ancillary Laws
Conclusion
Der War of aggression occupies a central position in international and national legal systems. While international law and national criminal law comprehensively punish the conduct and preparation of a war of aggression, the prohibition of the war of aggression in particular forms a core principle of the current international legal system for the protection of peace and the sovereignty of states. The legal frameworks on wars of aggression serve as an important foundation for international security architecture and as a bulwark against the use of military force contrary to collective security interests.
Frequently asked questions
Under what conditions is a war of aggression considered illegal under international law?
A war of aggression is expressly considered unlawful under Article 2(4) of the Charter of the United Nations, as the use or threat of force in international relations is fundamentally prohibited. Thus, military attacks by one state on another generally constitute a serious violation of the prohibition of force. Only two narrowly limited exceptions apply: the existence of a Security Council mandate under Chapter VII of the UN Charter for the maintenance or restoration of international peace and security, and the right to individual or collective self-defense under Article 51, if an armed attack occurs. If neither of these justifications exist, the use of military force constitutes a war of aggression and thus an unlawful act under international law.
What criminal consequences does a war of aggression have for the persons involved?
Under international criminal law, the waging of a war of aggression is classified as the so-called crime of aggression and thus constitutes an individually punishable act. According to the Rome Statute of the International Criminal Court (ICC), particularly Article 8bis, a person can be prosecuted if they participate in the planning, preparation, initiation, or execution of a war of aggression. The prerequisite is that the individual is actually capable of decisively influencing the political or military actions of a state (‘leadership position’). Under German criminal law, according to § 13 of the International Criminal Code (VStGB), the preparation and conduct of a war of aggression are also punishable. Responsible persons, usually high-ranking political and military decision-makers, can thus be held accountable before both international and national courts.
How is a war of aggression prosecuted by international courts?
International courts such as the International Criminal Court (ICC) are authorized to prosecute the crime of aggression, provided the formal requirements are met—in particular, that the respective state has ratified the Rome Statute and made the necessary declaration of jurisdiction. Proceedings are conducted under a precisely defined process: the ICC Prosecutor may initiate investigations, but for the crime of aggression, a preceding determination by the UN Security Council or corresponding investigations by the ICC’s Pre-Trial Chamber are required. Convictions are only handed down when individual guilt is established beyond reasonable doubt. Since not all states are subject to the ICC, prosecution may be limited; however, individual states can also act independently at the national level.
Can self-defense serve as justification for a war of aggression?
The right to self-defense is generally recognized in international law but is interpreted strictly. A military operation—even an offensive one—is only legally sanctioned if an armed attack has actually occurred against one’s own state or an allied state. The act of self-defense must also be proportionate, necessary, and immediate in response to the aggression. Preemptive strikes—so-called preemptive self-defense—are, according to prevailing legal opinion and the practice of the UN Security Council, not permissible unless the attack is imminent and unavoidable. If a state abuses the right of self-defense to justify a war of aggression without an actual attack, such use remains unlawful.
What role does the United Nations Security Council play in the context of a war of aggression?
According to Chapter VII of the UN Charter, the Security Council has primary responsibility for the maintenance of international peace and security. If it determines the occurrence of a war of aggression, it may authorize measures up to and including military enforcement actions against the aggressor state. Importantly, only the Security Council has the exclusive authority to authorize collective measures against a state—such as sanctions or the use of armed forces. However, the effectiveness of such measures depends on the consensus of the permanent members, since each holds a veto right. If a veto is exercised, measures can be blocked, making the enforcement against a war of aggression more difficult.
How do war of aggression and armed conflict differ legally?
If an armed conflict involves the use of military means, this does not necessarily mean that a war of aggression exists under international law. A war of aggression requires a deliberate, serious, and unjustified violation of the prohibition of force, and, in particular, at the level of political leadership, a planned, comprehensive act of aggression. Minor border incidents, civil wars, or internal armed conflicts without cross-border elements do not legally fall under the term war of aggression, but may constitute other violations of international law, such as war crimes or humanitarian abuses.
What legal options do states have to defend themselves against a war of aggression?
States can invoke international law, particularly the right of self-defense under Article 51 of the UN Charter, as long as the Security Council has not taken action. In addition, they can counter the attack through diplomatic means, by mobilizing international support and sanctions, or by bringing the case before international courts such as the International Court of Justice (ICJ) or the International Criminal Court (ICC). Lastly, they can seek support from alliance partners, provided collective security systems—such as NATO—apply. Any measures taken must always comply with applicable rules of international law to avoid committing further violations themselves.
