In scientific and legal literature, there are several definitions of these concepts: the theory of 'nominalism,' arguing that a nation can be considered a group of people who consider themselves a nation; 'naturalism,' where a nation is a historically formed group of people; 'voluntarism' - a voluntarily united group of people who consider themselves one nation. Proponents of the 'territorial principle' assert that a nation is a group of people compactly living in a certain territory. There is the 'linguistic principle,' which holds that a nation can be considered people speaking the same language. According to the value principle, a nation is formed by people who share certain moral and ethical values. The 'goal theory' states that a nation is a group of people with a common history and a common mission. Paul Gilbert, author of the fundamental study 'The Philosophy of Nationalism,' expresses the opinion that a nation can only be considered a group of people who claim to create their own state.
Also, there are no criteria that allow classifying a particular community as a people entitled to claim the creation of an independent state. For example, a religious-ethnic minority that tries to secede from a multinational state. Leaders of such movements prefer to consider the countries from which they are trying to secede as enslaving empires. Quite often they a priori reject the very principle of a multi-ethnic state, preferring to create a mono-ethnic state.
In 1991, the Organization of Unrepresented Nations was created. Among its founders were representatives of peoples who inhabited the USSR: Armenians, Crimean Tatars, Tatars, Latvians, Estonians, and Georgians. Currently, the Organization of Unrepresented Nations includes 69 ethnic groups and minorities, numbering more than 150 million people. Among them are peoples living in the territories of the former USSR: Tatars, Talysh, Bashkirs, Chechens, Assyrians, Chuvash, Circassians, Crimean Tatars, Mari, Komi, Udmurts, Buryats, Tuvans, and Gagauz. Among the members are two Kurdish organizations and Taiwan, de facto an independent state. These peoples, extremely diverse in many parameters, have one unifying link: their representatives are not part of leading international organizations, such as the UN. The Charter of the Organization of Unrepresented Nations states that the activities of this structure are based on five main principles: non-violence, human rights, self-determination and democracy, environmental protection, and tolerance. Over a decade and a half, six founders of the Organization managed to create their own states - independent Georgia, Armenia, Estonia, Latvia, Palau, and East Timor (Timor-Leste) appeared on the political map of the world.
In 1992, the UN General Assembly adopted the Declaration on the Rights of Persons Belonging to National or Ethnic, Religious and Linguistic Minorities. Article 1 of the declaration states: "States shall protect the existence and identity of national or ethnic, cultural, religious and linguistic minorities within their territories and shall encourage conditions for the promotion of that identity." In the vast majority of cases in the 20th century, large states recognized the unique characteristics of small peoples living on their territory in various ways. They were granted certain cultural and linguistic rights, and in some cases autonomy. 
Montserrat Guibernau, author of the book 'Nations without States,' points out that in the conditions of modern Western civilization, many peoples prefer not to fight for the formation of their own nation-states. In her opinion, this is due to the democratic changes that have taken place in Western countries: the nation-state was originally needed primarily to preserve the cultural and linguistic identity of small peoples. If the 'mother' state granted them such rights, the struggle for national self-determination lost its appeal. Guibernau emphasizes that separatist sentiments in many countries of Europe and North America will likely exist for an indefinite period, but they have no chance of turning into powerful national liberation movements. Currently, such views are shared mainly by a few radicals.
Michael Keating, author of the book 'Multinational Democracy: Peoples Without States in the Post-Sovereign Era,' notes that in recent decades the link between a people and a state has been broken. One people does not necessarily create a state, while the state does not guarantee happiness and prosperity to the people that formed it. Moreover, in some cases, a state turns out to be unnecessary for achieving prosperity, ensuring security, and maintaining order. Democracy also cannot be considered a necessary condition for the creation and existence of states. Keating is confident that in the foreseeable future, states will not disappear, but the world will change - it will be a complex and often contradictory system of distribution of power. He notes that peoples who currently do not have their own state risk never obtaining one in this situation.
Gidon Gottlieb, author of the book 'Nation Against State,' notes that in the 20th century, great powers allocated territories and allowed the creation of new states based on the principle of the right to self-determination. All such redrawings took place after the end of the three largest conflicts - two world wars and the Cold War. However, only once - after the end of World War I - such decisions were made collectively by all the great powers (Russia, where the Bolshevik revolution took place, participated in this process indirectly - it, for example, granted independence to Finland). In Gottlieb's opinion, most of the current national and ethnic conflicts cannot be resolved by redrawing state borders and allocating each people its own state.
There are several dozen self-proclaimed states in the world, which, however, the international community does not consider as such. For the most part, these are ethnic enclaves that have broken away from "mother" countries. According to the Institute for the Study of Self-Determination, operating under Princeton University, self-proclaimed states justify their claims to independence in various ways. As a rule, they argue that a community of people united by religion, language, culture, etc., has historically developed on this territory, and they do not see their future as part of another state. Such arguments carry particular weight if an independent state once existed on that territory. However, those opposing granting independence use similar evidence. For example, opponents of Palestinian independence argue that the Palestinian people have never existed, nor has a state by that name.
Such debates arise in almost all cases when it comes to recognizing or not recognizing a new state entity. The reason for this is the ambiguity of modern international law. For example, in 1975, the Helsinki Conference on Security and Cooperation in Europe proclaimed the principle of inviolability of state borders established after the end of World War II. On the other hand, the UN International Covenant on Civil and Political Rights (entered into force in 1976) declares the right of peoples to self-determination. The International Court of Justice also issued a verdict in 1975, according to which the right to self-determination belongs not to states but to individual citizens. A well-known specialist in international law, Marc Weller, a fellow at the University of Cambridge, calls this paradox the "self-determination trap."
Karen Parker, author of the book "The Case for Self-Determination," notes that modern international law cannot unequivocally answer the question: what needs to be done to create a new state. In the 20th century, as a result of the collapse of colonial empires, the so-called "declarative" method emerged - that is, a certain territory simply declares that it is an independent state. The traditional path - the so-called "constitutional" one - is more complex. It declares that for self-proclaimed states to acquire full status, international recognition is necessary. A formal act of diplomatic recognition means that one state accepts the independent status of another and the authority of its government.
There are two types of official recognition: de facto and de jure. De facto recognition (that is, based on the existence of a given structure) is informal in nature, but it is sufficient for both states to establish diplomatic relations, mutually recognize passports and visas, etc. De jure recognition (that is, based on existing international norms) provides for the establishment of interstate relations in full. Sometimes de facto recognition precedes de jure recognition. For example, Great Britain de facto recognized the Bolshevik government as the legitimate authority of Russia in 1921, and de jure only three years later.
Recognition is also necessary if power in a country changes in an unusual way - for example, as a result of a coup, revolution, or external invasion. The Taliban government, which de facto controlled most of Afghanistan from 1996 to 2001, was recognized by only three countries in the world, while the government it overthrew, which controlled no more than 12% of the country's territory, was recognized as legitimate by more than 70 states.
In June 1940, Soviet troops occupied Latvia, Lithuania, and Estonia. These countries lost their statehood and were incorporated into the USSR as union republics. The United States did not recognize the legitimacy of these actions by the USSR and considered the Baltic countries independent but occupied states. The embassies of these republics continued to operate in Washington, despite protests from Moscow.
Interestingly, the United States now includes previously independent countries. For example, the Confederate States of America, which emerged in 1861 and disappeared after defeat in the Civil War, was officially recognized by one of the German dwarf states. The Republic of Texas, which existed on the political map of the world from 1836 to 1845, was recognized by five countries. Some Indian tribes, and Hawaii, were also previously independent states, but are now considered peoples without their own statehood.