Based on the level of respect or formality, you can say "Korea is a wonderful country" in Korean in 3 ways:

• Informal: hangug-eun daedanhan nara-ya. (한국은 대단한 나라야.)
• Formal: hangug-eun daedanhan nara-yeyo. (한국은 대단한 나라예요.)
• Very formal: hangug-eun daedanhan nara-imnida. (한국은 대단한 나라입니다.)