Firstly, Chinese is never a pure culture in the history.
And yes, there are difference between the map of Han and Qing in the 2000 years,
The map of modern China is based on the bequest of Qing Dynasty which is built by Manchu.
Manchu conquered China and some border areas in 300 years and mixed them together. Finally, Manchu mixed themselves to Chinese after 1911.

http://en.wikipedia.org/w/index.php?title=File:Empire_of_the_Great_Qing_(orthographic_projection).svg&page=1
Sappho wrote on Nov 6
th, 2012 at 4:07pm:
Bowen wrote on Nov 6
th, 2012 at 3:42pm:
Between about 200BC and about 200AD, China is an united dynasty Han.
Oh... are you saying that to be Chinese is to be Han?
See below for what Han China was...
http://upload.wikimedia.org/wikipedia/commons/thumb/b/b0/Han_foreign_relations_C...Map of the world as known to Han Dynasty China in 2 CE. Names of non-Chinese peoples and states have been purposely left with their Chinese names (e.g. Dayuan instead of Fergana; Gaogouli instead of Goguryeo) to reflect the fact that our knowledge of participants in the Han world order comes almost exclusively from Chinese sources. (picture and description from Wiki)
And now have a look at what Han China is
http://www.travelchinaguide.com/images/map/china/china-map-9.jpg Han Chinese constitute about 92% of the population of the People's Republic of China (mainland China)
(map and text from Wiki)
It took a lot of ethnic cleansing by the Han peoples so as to enjoy a monocultural and almost pure ethnic existence that is your Han China of today.
What happened to the other cultures and ethnic groupings? Well... some suffered genocide so that we have no trace beyond what the Han Chinese wrote of them... most other ethnic groups were pushed out of their home lands and now represent Asians of other nations.