Relationship between International Law and Municipal:
International Law is the law which governs the relations of sovereign independent States inter se Municipal law or State law or national law is the law of a State or a country and in that respect is opposed to International Law which consists of rules which civilized States consider as binding upon them in their mutual relations. Kelsen observes that national law regulates the behavior of individuals International law the behavior of States or as it is put whereas national law is concerned with the international relations the so called domestic affairs of the State. International Law is concerned with the external relations of the State its foreign affairs.
There is a divergence of opinion on the question as to whether International Law and Municipal Law on the various national laws can be said to form a unity being manifestations of a single conception of law or whether International Law constitutes an independent system of law essentially different from the Municipal Law. The former theory is called monistic and the latter dualistic.
Monistic Theory: It maintains that the subject of the two systems of law namely, International Law and Municipal Law are essentially one in as much as the former regulates the conduct of States, while the latter of individuals. According to this view law is essentially a command binding upon the subjects of the law independent of their will which is one case is the States and in the other individuals. According to it International Law and Municipal Law are two phases of one and the same thing. The former although directly addressed to the States as corporate bodies is as well applicable to individuals for States are only groups of individuals.
According to the dualist view the systems of International Law and Municipal Law are separate and self contained to the extent to which rules of the one are not expressly or tacitly received into the other system. In the first place they differ as regards their sources. The sources of Municipal Law are customs grown up within the boundaries of the State concerned and statutes enacted therein while the sources of International Law are customs grown up within the Family of Nations and law making treaties concluded by its members. In the second place Municipal Laws regulates relations between the individuals under the sway of a State or between the individuals and the State while International Law regulates relations between the member States of the Family of Nations. Lastly there is a difference with regard to the substance of the law in as much as Municipal Law is a law of the sovereign over individuals while International Law is a law between sovereign State which is arrived at an agreement among them. The latter is therefore a weak law.
Besides the above two theories, Starke makes reference to two other theories namely, the Transformation Theory and Delegation Theory.
According to this theory it is the transformation of the treaty into national legislation which alone validates the extension to individuals of the rules set out in international agreements.
The transformation is not merely a formal but a substantial requirement. International Law according to this theory cannot find place in the national or Municipal Law unless the latter allows its machinery to be used for that purpose.
This theory is fallacious in several respects. In the first place its premise that International Law and Municipal Law are two distinct systems is incorrect. In the second place the second premise that International Law binds States only whereas municipal law applies to individuals is also incorrect for International Law is the sum of the rules which have been accepted by civilized states as determining their conduct towards each other and towards each others subjects. In the third place the theory regards the transformation of treaties into national law for their enforcement. This is not true in all cases for the practice of transforming treaties into national legislation is not uniform in all the countries. And this is certainly not true in the case of law making treaties.
Delegation Theory: According to this theory there is the delegation of a right to every State to decide for itself when the provisions of a treaty or convention are to come into effect and in what manner they are to be incorporated in the law of the land or municipal law. There is no need of transformation of a treaty into national law but the act is merely an extension of one single act. The delegation theory is incomplete for it does not satisfactorily meet the main argument of the transformation theory. It assumes the primacy of international legal order but fails to explain the relations existing between municipal and international laws.
It is settled by the leading English and American decisions that International Law forms part of the municipal law of those countries. The United States has unambiguously applied the doctrine that International Law is part of the law of the land. All international conventions ratified by the USA and such customary International Law as has received the assent of the United States are binding upon American Courts even if they may be contrary to the statutory provisions. There is a presumption in cases of conflict that the United States Congress did not intend to overrule International Law.