National identity is primarily associated with a person's citizenship because it reflects their legal relationship to a specific nation-state. Citizenship typically encompasses the rights, responsibilities, and identity that an individual holds in relation to their country. It signifies a formal recognition by the state that connects individuals to a nation, often leading to a sense of belonging and participation in the political, social, and cultural life of that nation. This connection is fundamental to the notion of national identity, as citizenship often acts as the basis for defining who is part of the national community.
While cultural affiliations, language skills, and income levels can influence how individuals relate to their national identity and may play a role in shaping cultural and social aspects of identity, they do not represent the defining legal and political status that citizenship does. Citizenship is the key factor that links individuals to their nation on an official level, making it the primary association with national identity.