When conflict broke out in 2009 with the Kokang, an ethnic-Han-Chinese minority, 37, 000 people fled to China, provoking sharp criticism of the Burmese junta.
In 2009 almost 200 people - mostly Han Chinese - were killed in deadly rioting.
Sure enough, ethnic-Han Chinese, many of them recent migrants hoping to profit from a train-related tourism boom, were the main targets of the violence in Lhasa.
For both the Uighurs and the Tibetans, economic development has been inseparable from immigration by ethnic-Han Chinese, 92% of China's population.
When protests erupted in Inner Mongolia after the death in May this year of an ethnic-Mongol herder allegedly when he was run over by a coal-lorry driven by an ethnic-Han Chinese the response in Mongolia itself was muted.
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Woeser, a Tibetan poet and blogger, says that some ethnic-Tibetan officials privately complain about the clampdown, but Han Chinese officials in Tibet toe a uniformly hard line.
During the night, a lorry driven by an ethnic Han Chinese driver hit one of the herders, called Mergen (single-named, like many Mongols).
"The race for luring the Chinese tourists is getting more and more competitive, " said Han Hwa-joon, head of the Korean Tourism Organization's China team.
Economic considerations are also coming into play -- it is significant that the initial rape rumors were spread by a Han Chinese angry that he lost his job in the factory where the Uighurs were working.
The Han Chinese are the country's dominant ethnic group, and the Uyghurs are a Turkic-speaking Muslim minority who consider Xinjiang their homeland.
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The Uighurs, Turkic-speaking Muslims who, like the Tibetans, have spent the last two millennia struggling against the Han Chinese, are already a minority in their own land.
The western regions have the highest proportion of non-Han minorities. (Uighurs and Tibetans outnumber the Han in Xinjiang and Tibet respectively, where they chafe under Chinese rule.) The regions have the least-secure parts of China's long borders.
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