Totally agree, it wasn't always "China", and there are many, many different tribes currently included in "Chinese". In fact, the current dominant ethic Han were not always the emperors, but I digress.
Here, let me google that for you:
http://en.wikipedia.org/wiki/H...
There's an amazing animated map on the right. The entire east/south of China has been "China" ever since, roughly, 300 BC (yep, that's 2300 years ago). The west (which, must I remind you, is nowhere as populated as the east, and certainly was even less populated before "modern China") was entirely conquered, or at least considered China, for the first time in roughly 1200 (800 years ago). Some fragments had been conquered and then lost previous to that, but whatever. In 1892, China occupied also all of current Mongolia, too, apparently.
Basically China as we know it is maybe new, but there has been mingling of population and wars over _thousands of years_. You could argue it belonged to.. different warring factions, or city-states, back in the days, but that's like saying the Italians had a bunch of city-states. As a whole though? The concept of "China" has been in the region considered China now for a long, long, long time. You can argue about Tibet, though it was conquered by Mongols in the 13th century, along with China and a lot of the Middle-East, and by the Qing in the early 18th century (http://en.wikipedia.org/wiki/History_of_Tibet#Manchurian_Qing_Dynasty). I mean... I don't know man, what do you want me to say? Those ethnic tribes considered "Chinese" have been sharing this territory for a couple hundred/thousands of years, and they've had a lot of wars, for sure, but that's no different than most old civilizations...
The point is, the current China has now joined the Western world's game of Diplomacy, and people are just unhappy at a new player. There is no historical reason to believe they would use their ICBMs more than the US or anyone else, and I can't blame them for wanting to play the game because they got screwed not playing it for the past hundred years.