If a State, which is protected by veto, considers itself to be powerful enough to deter other States from invoking the right to collective self-defence and resilient enough to survive measures taken against it, international law cannot effectively prevent it from attempting to change the territorial status quo by use of force. Even if the current weak system of international law cannot effectively stop such attempts, by using international law as a ‘gentle civilizer’ of the behaviour of States, as Kennan wrote, or as an institution for a saner international order, as Brierly wrote, including through putting pressure by implementing the five obligations above, and showing to the world the weakness of its legal justification, the rule of law may be able to retain its minimum force. Legal advisors should advise policy makers to take legally sound positions and, thus, contribute to the stabilisation of international relations based on international law. The 1970 Declaration mentioned Member States’ duty to cooperate for the realisation of the purpose of the United Nations. When faced with serious violation of the fundamental principles of the UN Charter, which are essential for peace, international lawyers have a collective duty to cooperate against the violation.