Türkiye’s Practice Concerning Preemptive Self-Defense under Customary International Law

Abstract

The expansion of cross-border threats posed by non-state armed groups has intensified legal debates concerning the scope of self-defense under customary international law, particularly where a state resorts to force before an anticipated attack has fully materialized. This article examines Türkiye’s reliance on preemptive self-defense in its cross-border military operations in northern Iraq and northern Syria and evaluates whether such practice is consistent with the requirements governing the use of force in international law. The study adopts a qualitative, descriptive-analytical legal approach and focuses on the distinction between self-defense in response to an armed attack, anticipatory or preemptive self-defense against an imminent attack, and preventive military action against more remote or speculative threats. Particular attention is given to the armed-attack threshold, imminence, necessity, proportionality, territorial sovereignty, self-defense against non-state armed groups, and the legal implications of the territorial state’s consent, inability, or objection. Türkiye’s operations against the Kurdistan Workers’ Party in northern Iraq and its military actions in northern Syria, particularly Operation Olive Branch and Operation Peace Spring, are examined as separate legal situations rather than as a single continuous practice. The findings indicate that the persistent existence of a security threat, the terrorist designation of an armed organization, or concerns regarding border security cannot independently justify the use of force within another state’s territory. Each operation requires an individualized assessment of the specific attack or threat, the evidence of imminence, the availability of less intrusive alternatives, and the scope and duration of the military response. The study further finds that Türkiye’s practice contributes to ongoing international debate concerning self-defense against non-state actors but is insufficient, by itself, to establish a general customary rule authorizing preemptive or preventive military action. Accordingly, preemptive self-defense must remain narrowly interpreted and clearly distinguished from preventive uses of force based on uncertain future threats.