國家的Adjective/People?

UK = He is a Britain/British/ people
Hk used to be a british colony _adj
USA = He is an American/ people
He plays american football. - adj

People and adjective spell the same but people - we normally use Capital Letter American, British, Britain.
Adjective = small case liek british passport, american football, australian wine etc.

The United Kingdom/Britain --> British (used for adjective and people)

The United States of America --> American (used for adjective and people)