* It's part of a proper noun:
* The United States of America is a powerful nation.
* I visited the United Kingdom last year.
* The Nation of Islam is a religious organization.
* It's used as a formal title:
* Nation is the title of a book or a movie.
* The Nation magazine is known for its liberal views.
You don't capitalize "nation" when:
* It's used as a common noun:
* Many nations participated in the conference.
* The nation is facing economic challenges.
* It's part of a phrase that isn't a proper noun:
* We are a diverse nation with a rich history.
* The nation's economy is in flux.
In short, capitalize "nation" when it's part of a specific, named entity (like a country) or a formal title. Otherwise, use lowercase.