Русско-англо-русский юридический словарь

A treaty is an agreement under international law entered into by actors in international law, namely sovereign states and international organizations. A treaty may also be known as an (international) agreement, protocol, covenant, convention, pact, or exchange of letters, among other terms. Regardless of terminology, all of these forms of agreements are, under international law, equally considered treaties and the rules are the same. (Wikipedia)

In general, to be a national is to be a member of a state. Nationality is acquired by birth or adoption, marriage, or descent (the specifics vary from country to country). Having a nationality is crucial for receiving full recognition under international law. Indeed, Article 15 of the Universal Declaration of Human Rights declares that “Everyone has the right to a nationality” and “No one shall be arbitrarily deprived of his nationality nor denied the right to change his nationality” but is silent on citizenship. Citizenship is a narrower concept: it is a specific legal relationship between a state and a person. It gives that person certain rights and responsibilities. It does not have to accompany nationality. In some Latin American countries, for example, such as Mexico, a person acquires nationality at birth but receives citizenship only upon turning 18: Mexican children, therefore, are nationals but not citizens. (The Economist)

President Xi Jinping claims China has a historic right of ownership to almost the entire South China Sea, despite a 2016 international arbitration ruling saying Beijing's claim had no legal basis under international law. (Daily Express)