The rules of jus cogens (also known as pre-emptory norm) are derived from the customary international law, and it is a rule or principle which is so fundamental that it binds all states and does not allow any exceptions. They are ‘accepted and recognized by the international community of States as a whole which can be modified only by a subsequent norm of general international law having the same character’. Article 53 of the Vienna Convention on the Law of Treaties (VCLT) 1969 states as follows:
“a treaty is void if, at the time of its conclusion, it conflicts with a pre-emptory norm of general international law’”
Article 64 of the Vienna Convention on the Law of Treaties 1969 gives a retrospective effect to the provision of Article 53 and further enhances its importance. With this, even an existing treaty stands void if it comes in conflict with a pre-emptory norm.
Natural law also stood as a prominent character in the development of jus cogens in international law. However, the concept of jus cogens is purely based on social construction even if the foundation of the concept is on shaky grounds.
The concept of jus cogens was said to be popularised by Verdross. He defined it as the ‘ethical minimum recognized by all the states of the international community’, which includes the obligation to undertake certain ‘moral task’, such as ‘maintenance of law and order within states, defense against external attacks, care for the bodily and spiritual welfare of citizens at home, and protection of citizens abroad’. It, as pointed out by Lauterpacht in the case of Bosnia and Herzegovina v Serbia and Montenegro, jus cogens also operates as a concept superior to both customary international law and treaty. Although this concept is important, the International Law Commission remarked that ‘there is no simple criterion by which to identify a general rule of international law as having the character of jus cogens’.
Also, as noted by Yasseen, a State or a minority number of States which refuse to accept the peremptory character of the rule, the acceptance and recognition as jus cogens by all other States would not be affected, because a mere majority would suffice, and the minority States will not be able to opt out for long as they will loss certain privileges.
Nonetheless, the rules of jus cogens consist of several significant elements in the international legal context. The rules of jus cogens which were made of standards laying down international obligation are so essential for securing the fundamental interest of the international community that any breach of the same was considered to be a crime by that community as a whole. The same has now been envisaged in the provision laid down in Article 40 of the Draft Articles on Responsibility of States for Internationally Wrongful Acts 2001. The use of force against the other territory was held by the International Court of Justice in Nicaragua v USA as wrongful act under the jus cogens rules. In addition to the same, slave trade, genocide, racial discrimination and apartheid are also covered under the category of wrongful acts within the contemporary of jus cogens rules.
Moreover, in the case of Prosecutor v Anto Furundzijaṅ, it was stated as follows:
“jus cogens has meta-legal effect which has a deterrent effect. in that it signals to all members of the international community and the individuals over whom they wield authority that the prohibition is an absolute value from which nobody must deviate.”
A similar provision is also laid down in the Swiss Constitution, Article 139(2) wherein it states that if the law of nation violates the international law, the Federal Assembly shall declare it invalid, whether as a whole or in part.
After analyzing the above statements, it can be said that jus cogens acts as a protective shield for upholding the human dignity and rights. Criddle and Fox-Decent stated that the jus cogens rules will trigger the fiduciary principle, where any entity and States that assume unilateral administrative power over individuals bears a fiduciary obligation to honor the basic demands of dignity, which includes the peremptory norms of international jus cogens’. As mentioned above, any activities or treaties carried out by the States or international organisations which offend human dignity and rights are contrary to the concept of jus cogens and will be considered null and void.
Jus cogens has also an effect on the doctrine of state immunity. The general rule is that all States have the immunity from being sued by the others. This can be clearly seen in Al-Adsani v. UK, where the claimant brought an action for damages in tort against the Kuwait government, claiming that he has been tortured by the officials of Kuwait. It was held that the government of Kuwait was entitled to immunity from being sued.
The central issue is whether laws of one state can ever be subordinate to the laws of a community of states. There's a growing sense that if one state passes laws that violate these norms, other states can simply gang up on that state without needing cover from international law. As a general rule, I think we need to be careful about making it seem like a "majority" opinion is more accurate than a "minority" opinion. The truth is that states generally interpret international law in ways that benefit their political cause, and so-called experts voice their opinions that are greeted with cynical skepticism. Some peremptory norms define criminal offences which are considered to be enforceable against not only states, but individuals as well.
  ICJ 2
 Case Concerning Military and Paramilitary Activities In and Against Nicaragua, ICJ Reports 1986
 Evan J. Criddle and Evan Fox-Decent, ‘A Fiduciary Theory of Jus Cogens’, The Yale Journal of International Law [Vol.34]
 (2002) 34 EHRR 273