This is the 511th most frequent Korean word.
중국은
"China is"
Here, '중국은' is the topic marker phrase for 'China', using '은' to emphasize 'China' as the subject or topic.
중국은 큰 나라입니다.
China is a big country.
In this example, '중국은' highlights 'China' in the sentence as the particular topic being commented on related to the first visitation.
중국은 내가 처음 방문한 아시아 국가였어요.
China was the first Asian country I visited.
Here, '중국은' introduces 'China' as the topic, setting up the statement about its history.