International law generally prohibits the use of force except in specific, narrowly defined circumstances. Under Article 51 of the UN Charter, a state may use force in self-defence only if an armed attack occurs. This has traditionally excluded pre-emptive strikes, which involve using force before an attack has actually happened, based on perceived threats. However, some argue that customary international law allows anticipatory self-defence, especially if the threat is imminent, overwhelming, and leaves no choice of means, as outlined in the Caroline case (1837).

Despite this, the concept of pre-emptive self-defence remains controversial, particularly when used to justify unilateral military action without clear UN authorization. The 2003 Iraq invasion by the U.S. and its allies reignited debate, as it was framed as pre-emptive but lacked Security Council approval and clear evidence of an imminent threat. Most legal scholars and states remain cautious, emphasizing that expanding the self-defence doctrine risks undermining the UN Charter framework and encouraging abuse. Thus, international law permits pre-emptive strikes only in exceptional, narrowly interpreted cases, and generally favors collective security mechanisms over unilateral action.

International law generally prohibits pre-emptive strikes under the **UN Charter**, which allows the use of force only in cases of **self-defense against an armed attack** (Article 51) or with **UN Security Council authorization**. A pre-emptive strike—using force before an actual attack occurs—is controversial because it challenges the principle of state sovereignty and the prohibition on the use of force (Article 2(4)). While some argue that pre-emptive self-defense may be justified if an attack is **imminent, overwhelming, and leaves no choice**, this remains a debated and largely unsettled issue in international law, with most scholars and states considering it illegal unless under extreme necessity.