Core Legal Answer & Context: The right to self-defence is a fundamental principle in international law, allowing states to use force in response to an armed attack. The question of whether this right extends to 'pre-emptive' or 'anticipatory' self-defence (using force before an actual armed attack has occurred) is highly contentious and generally not recognized as a broad right.

Relevant Statutes and Sections:

1. UN Charter, Article 2(4): Prohibits the threat or use of force against the territorial integrity or political independence of any state.
2. UN Charter, Article 51: Recognizes the inherent right of individual or collective self-defence "if an armed attack occurs." The phrase "if an armed attack occurs" suggests a reactive right, not a pre-emptive one.

Traditional View (Caroline Doctrine):

1. The Caroline Incident (1837), a diplomatic exchange between the US and UK, established a strict test for anticipatory self-defence: the "necessity of self-defence is instant, overwhelming, leaving no choice of means, and no moment for deliberation." This sets a very high threshold, allowing for action only in the face of an imminent attack.

Modern Interpretations (Controversial):

1. Some states argue for a broader right to pre-emptive self-defence, particularly against non-state actors or in the face of threats involving weapons of mass destruction, where waiting for an attack could be catastrophic. This is often termed 'preventive war' or 'pre-emptive strike.' However, this interpretation is widely criticized as it could undermine the prohibition on the use of force and lead to abuse, potentially justifying unilateral military action without clear evidence of imminent threat.

Important Landmark Cases:

1. Oil Platforms Case (Iran v. United States, ICJ, 2003): The ICJ reiterated that for self-defence to be lawful, there must be an "armed attack" and the response must be necessary and proportionate. The Court did not endorse a broad right to pre-emptive self-defence, emphasizing the strict conditions for the use of force.

Clear Conclusion: Under current international law, the right to self-defence (Article 51) is generally understood as a reactive right to an armed attack that has occurred. While a narrow interpretation of anticipatory self-defence (meeting the strict Caroline Doctrine criteria) might be permissible, a broad right to 'pre-emptive action' or 'preventive war' is not recognized and remains highly controversial, as it risks violating the fundamental prohibition on the use of force.