Inspired by this question over at EL&U.
In my research for a response that question (which I never posted), I found this article in the Economist, which includes this paragraph:
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.
I was born in the US, so I am a US citizen and a US national. At what stage of the immigration process can an immigrant to the US truthfully and legally declare the US as their nationality?
(Limiting this to the US since different countries handle citizenship and nationality differently.)