The concept of an “act of war” has evolved significantly in international law, shaped by changing legal frameworks, political realities and the decline of formal war declarations. This analysis traces its historical trajectory and explores how Pakistan can safeguard its strategic interests while adhering to international legal principles.
In ancient civilizations such as Greece, Rome and China, warfare was guided by customs rather than codified laws. The Roman concept of bellum justum (just war) required both a formal declaration and moral justification. During the Middle Ages, issuing formal declarations became a key marker of lawful warfare. Legal scholars like Hugo Grotius later developed these ideas into a coherent doctrine, establishing that a declaration of war suspended peacetime obligations and triggered a distinct legal regime—the law of war.
This framework eroded after the World Wars of the 20th century. The 1945 UN Charter fundamentally altered the legal landscape, prohibiting the use of force under Article 2(4) and recognizing only two exceptions: the inherent right of self-defence and Security Council-authorized enforcement under Chapter VII. In this post-Charter era, states have moved away from formal war declarations, instead framing military actions as “self-defence,” “armed attack,” or “countermeasures.” Consequently, the term “act of war,” while influential politically, has diminished in legal precision and normative significance.
Even without formal definition, “act of war” overlaps with the concept of aggression. UN General Assembly Resolution 3314 (1974) identifies acts such as invasion, bombardment or blockades as aggression, potentially triggering the right of self-defence under Article 51. Legal assessment now focuses on the gravity, scale and consequences of an act rather than its label. International humanitarian law (IHL) reflects this functional shift: Common Article 2 of the 1949 Geneva Conventions applies to any armed conflict between states, irrespective of declarations. The International Court of Justice affirmed this in Nicaragua v. United States (1986), noting that armed conflict is determined by objective criteria, not terminology.
Since the early 2000s, the phrase has resurfaced in new contexts. Following the 9/11 attacks, US officials termed them an “act of war,” framing counterterrorism operations under Article 51. This interpretation extended the use-of-force concept to non-state actors, a perspective still debated internationally. Similarly, cyber operations have prompted discussion on whether cyberattacks may qualify as acts of war. The Tallinn Manual suggests cyberattacks causing kinetic effects can, in some cases, be considered armed attacks under Article 51.
In South Asia, the term carries particular weight, as India and Pakistan have faced repeated military crises without formal war declarations. After the 2019 Pulwama attack, India conducted airstrikes in Balakot. Pakistan condemned the strikes as a grave violation of sovereignty but did not label them as an act of war. Conversely, India described Pakistan’s retaliatory aerial engagement over the Line of Control as a hostile response warranting restraint, not war.
The May 2025 military escalation followed a similar pattern. Pakistan emphasized violations of its territorial sovereignty, while India described Pakistan’s response as escalatory. Both sides avoided formal war declarations, reflecting the understanding that declaring war triggers obligations, diplomatic ruptures and economic costs, including mobilization of forces, reservist call-ups, rising insurance and fuel costs, airspace restrictions and limitations on port access. Post-UN Charter norms also encourage states to avoid appearing as violators of international law, as seen in Russia’s designation of its 2022 invasion of Ukraine as a “special military operation.”
The Indus Waters Treaty (IWT) highlights the strategic use of war rhetoric. After India held the treaty in abeyance, Pakistan warned that any attempt to divert water would be treated as an “act of war.” Domestically, this consolidates public support, reinforces narratives of sovereignty under threat and justifies military and diplomatic readiness. Internationally, it signals that violations of transboundary water obligations could destabilize regional peace.
However, invoking the term carries legal and strategic risks. Treaty breaches constitute serious violations, but the legal basis for invoking self-defence under Article 51 remains debated. Premature or uncalculated declarations may limit policy options, weaken deterrence if no action follows or escalate tensions unnecessarily. Therefore, such declarations must be made with caution, ensuring readiness politically, diplomatically and militarily.
In conclusion, while “act of war” retains rhetorical significance, its practical legal relevance is limited. International law now emphasizes aggression, armed attacks and objective assessments over formal war declarations. Yet in strategic contexts such as Pakistan-India relations, invoking the term can signal resolve, galvanize domestic audiences and project Pakistan’s readiness to protect its sovereignty. Even within legal and strategic constraints, carefully calibrated use of this language demonstrates determination to safeguard national interests and respond decisively to perceived threats.
—The writer is a regular contributor to the national press.
