国家 guó jiā

The term for "country" or "nation" in Mandarin Chinese is guó jiā.

Example:

Dōng nán yà guó jiā lián méng yǒu shí gè chéng yuán guó. 
The Association of Southeast Asian Nations has ten member states.

Traditional Characters:
東南亞國家聯盟有十個成員國｡
Simplified Characters:
东南亚国家联盟有十个成员国｡