Zhongguo, or the Central Nation is the world's most populous country and its oldest continuos civilization.
The term Zhongguo is often held up as proof of the Chinese people's general view of themselves as the center of the world. Although Chinese ethnocentrism is of course present, as it is in every culture, the term Zhongguo does not actually reflect this. I have been told that the term originally does not refer to China being in the center of the world, but rather it refers to a time, around the Shang or Zhou Dynasties when many different groups of people, all roughly what we would call Han. However, only the people in the central area were developing the system of writing and other implements of urban culture. It was these six or seven central states that were called "the Central Kingdoms" by the outlying people, and from which the name Zhongguo comes. Or at least this is one story I have been told.
The name "China" is somewhat problematic, since it derives from the radical and not very well liked Qin Dynasty, which ruled for 21 brief, bloody years 2200 years ago. Continuing to refer to Zhongguo as "China" is somewhat akin to people millenia hence calling Germany "Naziland".
That being said, in most of my write ups, I do say "China" or "Chinese" and not "Zhongguo" , "Zhongwen" , "Zhongguoren" and the like.