The original inhabitants of a country

One word substitute is Aborigines.

Aborigines: a person, animal, or plant that has been in a country or region from earliest times.
Citizens: a legally recognized subject or national of a state or commonwealth, either native or naturalized.
Natives: a person born in a specified place or associated with a place by birth, whether subsequently resident there or not.
Primitive: relating to, denoting, or preserving the character of an early stage in the evolutionary or historical development of something.