Montevideo Convention

The Montevideo Convention on the Rights and Duties of States is a treaty. Today, it is part of customary international law. The treaty was signed at Montevideo, Uruguay, on December 26, 1933, at the Seventh International Conference of American States. At this conference, United States President Franklin D. Roosevelt and Secretary of State Cordell Hull declared the so-called Good Neighbor Policy which opposed U.S. armed intervention in inter-American affairs. Franklin D. Roosevelt tried to reverse the perception of "Yankee imperialism" with this treaty. The view of Yankee imperialism was brought about by policies instituted (largely) by his predecessor, President Herbert Hoover. The convention was signed by 19 states, three with reservations (Brazil, Peru and the United States).
The convention is about what a state is and what rights and duties a state has. The most well-known is article 1, which sets out the four criteria for statehood that have sometimes been recognized as an accurate statement of customary international law:
In addition, the first sentence of article 3 states explicitly that "The political existence of the state is independent of recognition by the other states." This is known as the declarative theory of statehood.
Some have questioned whether these criteria are enough, as they allow less-recognized entities like the Republic of China (Taiwan) or under- or unrepresented entities like the Principality of Sealand, Somaliland or Liberland to claim full status as states. According to the alternative constitutive theory of statehood, a state exists only insofar as it is recognized by other states. It should not be confused with the Estrada doctrine.
Some people have attempted make the definition of statehood broader, although they have less support. Founders of non-territorial micronations often say that the requirement in the Montevideo Convention of a defined territory is unjust. Some non-territorial entities, notably the Sovereign Military Order of Malta, are considered subjects of international law, but they do not aspire to be states.
Signatories.
The states that signed this agreement are: Honduras, United States of America, El Salvador, Dominican Republic, Haiti, Argentina, Venezuela, Uruguay, Paraguay, Mexico, Panama, Guatemala, Brazil, Ecuador, Nicaragua, Colombia, Chile, Peru, Cuba.
The Montevideo Convention only codified existing norms, there is nothing "new" in the convention. For this reason, it does not only apply to those who signed it, but to all subjects of international law as a whole.
The European Union, in the principal statement of its Badinter Committee, follows the Montevideo Convention in its definition of a state: by having a territory, a population, and a political authority. The committee also found that the existence of states was a question of fact, while the recognition by other states was purely declaratory and not a determinative factor of statehood.
Switzerland, although not a member of the European Union, adheres to the same principle, stating that "neither a political unit needs to be recognized to become a state, nor does a state have the obligation to recognize another one. At the same time, neither recognition is enough to create a state, nor does its absence abolish it."