A contract is an official and explicit written agreement that states use to engage legally.  A treaty is an official document that expresses agreement in words; It is also the objective result of a solemn event that recognizes the parties and their defined relationships. The publication of a contract does not require academic accreditation or interdisciplinary background knowledge. Articles 46-53 of the Vienna Convention on Treaty Law define the only ways to declare treaties invalid – which is considered unenforceable and void in international law. A treaty is invalidated either because of the circumstances in which a State party has acceded to the treaty, or because of the very content of the treaty. Cancellation is separate from termination, suspension or termination (addressed above), all of which involve a change in the consent of the parties to a previously valid contract, not the nullity of that consent in the first place. The distinctions are mainly related to their method of authorisation. Contracts must be advised and approved by two-thirds of the senators present, but executive agreements alone can be executed by the President. Some contracts give the president the power to fill gaps through executive agreements rather than additional contracts or protocols.
Finally, agreements between Congress and the executive branch require the approval of the House of Representatives and the Senate before or after the president signs the treaty. Before 1871, the U.S. government regularly entered into contracts with Indians, but the Indians Appropriation Act of March 3, 1871 (Chapter 120, 16 Stat. 563) had a horseman (25 US. C No. 71), which effectively ended the drafting of presidential treaties by declaring that no Indian nation or Indian tribe can be recognized as a nation, tribe or independent power with which the United States can enter into contractual contracts. After 1871, the federal government continued to maintain similar contractual relations with Indian tribes through agreements, statutes and executive ordinances.  Initially, international law did not accept and reject reservations unless all parties accepted the same reservations. However, in order to encourage as many states as possible to join the treaties, a more straightforward reserve rule has been established. While some treaties still explicitly prohibit any reservations, they are now generally accepted to the extent that they are not incompatible with the objectives and objectives of the treaty.