International contract law has been largely codified by the Vienna Convention on Treaty Law, which sets out the rules and procedures governing the establishment, modification and interpretation of contracts, as well as the resolution and resolution of disputes and alleged infringements.  Treaties are considered to be one of the oldest manifestations of international relations as the main source of international law.  There are three ways to change an existing contract. First, a formal change requires that States Parties be forced to go through the ratification process again. The renegotiation of the treaty provisions can be long and time-consuming and often some parties to the original treaty will not become parties to the amended treaty. In determining the legal obligations of states, a party to the original treaty and a party to the amended treaty, states are bound only by the conditions on which they have agreed. Contracts may also be amended informally by the treaty office if the amendments are procedural in nature, and technical changes in customary international law may also alter a contract in which the state`s conduct presents a reinterpreting interpretation of legal obligations arising from the treaty. Minor corrections to a contract may be accepted by a minutes; However, a minutes are generally reserved for amendments to correct obvious errors in the adopted text, i.e. where the adopted text does not adequately reflect the parties` intention to adopt it. The end of the preamble and the beginning of the agreement itself are often referred to by the words “agreed as follows.” In the United States, the term “treaty” has a different, more limited legal meaning than in international law.
U.S. legislation distinguishes what it calls “treaties” from “executive agreements” that are either “executive agreements of Congress” or “single executive agreements.” Classes are all treatises of international law in the same way; they differ only in U.S. domestic law. A multilateral agreement is reached between several countries, which establishes rights and obligations between each party and each other party.  Multilateral treaties may be regional or involve states from around the world.  “Mutual guarantee” treaties are international pacts, for example. B the Treaty of Locarno, which guarantees each signatory the attack of another.  Article 46-53 of the Vienna Convention on Treaty Law establishes the only ways to declare treaties invalidable under international and non-applicable law.