Threat of force in public international law is a situation between states described by British lawyer Ian Brownlie as:
an express or implied promise by a government of a resort to force conditional on non-acceptance of certain demands of that government. The 1969 Vienna Convention on the Law of Treaties notes in its preamble that both the threat and the use of force are prohibited. Moreover, in Article 52, it establishes the principle that if threats of using force are made during diplomatic negotiations, then any resulting treaty is invalid, stating "A treaty is void if its conclusion has been procured by the threat or use of force in violation of the principles of international law embodied in the Charter of the United Nations".
Philosophical and legal roots The evolution towards prohibiting the threat of force has origins in historical legal and philosophical traditions.
Pre United Nations Charter
Just War Tradition to Law of Nations The legal scholarship on the use of force underwent a change, moving from the medieval just war tradition to the early modern Law of Nations (LN) and eventually the modern international law of the 20th century. While 19th-century international law conceded states the right to resort to force and war, this right was conditional and restricted. Force and war were simultaneously considered violations of states' inherent rights, such as their existence, self-preservation, internal sovereignty, external independence, equality, and dignity. Consequently, the use of force against a state was generally deemed a violation of one or more of these fundamental rights. Resort to force was typically considered permissible only after peaceful means of dispute settlement had failed or been refused.
Perpetual Peace Projects (PPP) Emerging in the late 16th century alongside the Law of Nations, these projects offered a contrasting philosophical approach. While the LN tradition primarily aimed to regulate interstate wars, the PPP's main goal was to abolish them. Proponents of perpetual peace, including thinkers like the Abbé de Saint-Pierre, Jean-Jacques Rousseau, and Immanuel Kant, advocated for international arbitration as the means for settling interstate disputes, envisioning an International Union that would either possess coercive power (strong variant) or function as a purely arbitral tribunal (weak variant). This tradition emphasized the link between "perpetual" and "peace" as a means to prevent war and establish a European society based on justice and freedom.
Pre-Charter Attempts at Restriction The Hague Peace Conferences of 1899 and 1907 marked the first serious interstate diplomatic attempts to restrict the recourse to war, aiming for the peaceful adjustment of international differences. During this period, the unlawfulness of ultimata and "measures short of war" gained increasing currency. The 19th-century principle of non-intervention was predominantly understood to interdict armed force, including the threat of force, though the law on this matter was not entirely settled.
The UN Charter Era (1945 onwards) The adoption of the UN Charter in 1945 was a milestone in the regulation of force, establishing a nearly fully-fledged ban on the use of force in international relations.
Drafters' Intent and Scope The Allied Powers, motivated by the shortcomings of the Kellogg-Briand Pact and the devastations of World War II, aimed to bolster the prohibition of warfare by adopting more stringent provisions. Their intent was to declare the independent use of armed force by any UN member clearly unlawful, except in cases of self-defence against aggression. Discussions during the San Francisco Conference came from a desire for an "absolute all-inclusive prohibition" with "no loopholes" for unilateral armed actions. Proposals to expand the prohibition to economic, moral, physical, or political force were rejected, solidifying its focus on military force. The duty to refrain from threatening force was intrinsically linked to the duty, enshrined in Article 2(4), to seek settlement of disputes only through peaceful means. The Charter's strict ban was designed to include actions previously known as "measures short of war". Article 2(4) expressly forbids "the threat or use of force." The International Court of Justice (ICJ) affirmed in its 1996 Nuclear Weapons Advisory Opinion that the threat of the use of force is just as unlawful as the actual use of force. This symmetrical prohibition generally means that if a particular use of force would be illegal, a threat to employ that force would also be illegal.
Philosophical Debate: Symmetry vs. Asymmetry The prevailing view among most states and supported by the ICJ is that the prohibition of the threat of force operates symmetrically with the prohibition of the use of force. Legal texts systematically prohibit both in the same manner and to the same extent, without separate criteria for lawfulness. A minority of scholars, notably Romana Sadurska in 1988, argued for a significant legal difference, suggesting that a threat of force is a "lesser international wrong" compared to actual use. This perspective posited that an "effective threat" could be an "economical guarantee against open violence" (e.g., nuclear deterrence), and threats made for certain law enforcement purposes might not be unlawful. However, this view has been widely critiqued for running counter to the drafters' intent for deterrence to be primarily channeled through the Security Council, and it has not been broadly accepted in state practice.
… excerpt ends here. Continue reading the full article.
