The concept “act of war” has experienced a significant shift in international law, influenced by changing legal frameworks, political realities, and the decline of formal declarations of war. This insight explores how the term “act of war” has evolved and considers how Pakistan can promote its strategic interests by responding within recognised international legal principles.
In ancient civilisations such as Greece, Rome, and China, warfare was governed by customs and procedures rather than codified legal frameworks. The Roman concept of bellum justum (just war) required both a formal declaration and a moral justification for the use of force. During the Middle Ages, the practice of issuing formal declarations before hostilities became an essential marker of lawful warfare.
During the early modern era, legal scholars such as Hugo Grotius advanced these concepts into a coherent doctrine of international law. For Grotius and his intellectual successors, a formal declaration of war marked a pivotal legal boundary, as it suspended peacetime obligations and triggered a distinct legal regime—the law of war.
This framework was dismantled following the Great World Wars of the 20th Century. The adoption of the UN Charter in 1945 established a general prohibition on the use of force under Article 2(4), marking a fundamental shift from war as a sovereign right to war being presumed illegal. The Charter recognises only two exceptions: the inherent right of self-defence and collective enforcement actions authorised by the Security Council under Chapter VII.
In this post-Charter environment, States no longer relied on declarations of war but instead used terms like “self-defence,” “armed attack,” or “countermeasures” to justify their actions within legally acceptable limits. As a result, the term “act of war”—although still influential in political rhetoric—has gradually diminished in legal precision and normative significance.
While the phrase lacks a formal legal definition, its substance overlaps with the concept of aggression. Under the 1974 UN General Assembly Resolution 3314, actions such as invasion, bombardment, or blockades qualify as aggression, potentially triggering the right of self-defence under Article 51. However, legal assessment now centres on the gravity, scale, and consequences of the act rather than its terminology.
International Humanitarian Law (IHL) has developed to respond to this functional shift. Common Article 2 of the 1949 Geneva Conventions stipulates that IHL applies to any “armed conflict” between states, irrespective of whether war has been officially declared or not. This pragmatic approach was confirmed by the International Court of Justice in Nicaragua v. United States (1986), where the Court highlighted that the existence of an armed conflict is determined by objective criteria, not by the terminology used by states.
Since the early 2000s, the use of “act of war” has resurfaced in new and controversial contexts. After the 9/11 attacks, U.S. officials described these attacks as an “act of war,” framing counterterrorism operations as exercises of self-defence under Article 51. This interpretation expanded the definition of “use of force” to include non-state actors, a viewpoint that is still debated among legal scholars and states.
Similarly, the emergence of cyber operations has initiated discussions regarding whether a cyberattack may be regarded as an “act of war.” Although there is no definitive threshold, the Tallinn Manual indicates that cyberattacks causing kinetic effects may, in some cases, qualify as armed attacks under Article 51.
The term “act of war” carries particular significance in the South Asian security context, where India and Pakistan have experienced recurrent military crises without the formal declaration of war. For instance, in 2019, following the Pulwama attack , India conducted airstrikes in Balakot. Pakistan condemned the strike as a grave aggression and a violation of Pakistan’s sovereignty, but notably stopped short of classifying it as an “act of war.”
Conversely, India framed Pakistan’s retaliatory action—which included the aerial engagement over the Line of Control and the downing of an Indian aircraft—not as an “act of war,” but as a hostile response that warranted restraint.
The military escalation between India and Pakistan in May 2025 raised similar questions regarding the thresholds of war. Pakistan’s official responses emphasised violations of its territorial sovereignty and blatant aggression by India. On the other hand, India publicly described Pakistan’s 9–10 May response as escalatory and provocative. Both sides, therefore, continued a strategic pattern of managing military engagement without declaring war.
The avoidance of the “war” narrative reflects the realisation that, once war is declared, certain obligations and consequences are triggered. Labelling an action as an "act of war" can lead to the severance of diplomatic relations. Economically, such a declaration imposes heavy costs: forces are mobilised, reservists are called up, prices and insurance rise, fuel supplies tighten, and air traffic is disrupted. Similarly, access to foreign ports may be denied under maritime safety rules, severely impacting trade and supply chains.
Furthermore, in the post-UN Charter framework, where the use of force is prohibited, states are particularly cautious about appearing to violate international law. By avoiding the term “war,” states aim to present themselves as responsible international actors operating within legal limits, as exemplified by Russia's designation of its 2022 invasion of Ukraine as a 'special military operation' rather than a war.
However, following India’s decision to hold the Indus Waters Treaty (IWT) in abeyance, Pakistan warned that any attempt to divert water flows would be treated as an “act of war”. Domestically, this framing consolidates public sentiment, reinforces narratives of sovereignty under threat, and justifies enhanced military and diplomatic preparedness. Internationally, it signals that tampering with transboundary water obligations is not a neutral act but rather can destabilise regional peace.
Yet invoking the term “act of war” in this context involves legal and strategic risks. Although treaty breaches can constitute serious violations of international obligations, the legal basis for invoking the right of self-defence under Article 51 of the UN Charter is still under development. This language may limit the state's policy options, where failing to act could weaken deterrence rather than strengthen it. Therefore, such declarations should be made with caution and only when the state is prepared—politically, diplomatically, and militarily—to bear the consequences.
Therefore, while the phrase “act of war” retains rhetorical significance, its practical relevance in legal terms is limited. In the context of the IWT, invoking war rhetoric may galvanise domestic audiences or demonstrate resolve; however, it also risks confining the state to rigid commitments.
Nonetheless, even with the strategic and legal constraints, the use of this language projects Pakistan’s determination to safeguard its national interests and indicates that it is prepared to respond decisively to any perceived threat.