On Monday, a worried UN -secretary general, Ban Ki-moon, urged China to use "extreme care" in dealing with violent protests. By then, however, it was too late. Scores of people had been killed in Urumqi, the capital of Beijing's Xinjiang region. Over the weekend, ethnic rioting erupted in the troubled inland city. Violence continued through Tuesday. The disturbances apparently started with a peaceful protest on Sunday over the deaths in June of at least two Uighur workers in southern Guangdong province. The victims, Turkic Muslims, were killed by Han, members of China's dominant ethnic group. Urumqi's Uighurs were outraged by, among other things, the failure of Guangdong authorities to bring the perpetrators to justice. Uighurs accuse Urumqi's police of savage attacks on demonstrators on Sunday. At this point it is difficult to say how the violence started, but it is clear that, sometime after the initial demonstration, Uighurs began attacking Han in the streets with sticks, bricks and knives. Enraged demonstrators set fires and overturned vehicles. The latest reports indicate that thousands of Han are now roaming the streets of Urumqi looking for revenge. The latest official death toll is 156, but undoubtedly more have died. How did this tragedy happen? "There were no warning signs about the riots," said Tang Yan, a 21-year-old pharmacy employee who fled rampaging Uighurs. "No one expected it." Though these disturbances may have come as a surprise to Ms Tang, they were all but inevitable. There have for centuries been Han living in what the Chinese today call Xinjiang, or New Frontier, which comprises one-sixth of the territory of present-day China. In the 1940s, the Han, an amalgamation of ethnicities, constituted about five per cent of Xinjiang's population. Today, their number has swollen to about 40 per cent. In the capital of Urumqi, the Han now constitute more than 70 per cent, a result of Communist Party programmes and incentives over the course of the past 60 years aimed at bringing Han settlers into the Muslim lands it administers. The Han take almost all the good jobs and business opportunities. Beijing strips the Uighur homeland of its mineral resources and best crops. There are Uighur officials in Xinjiang, but real political power is held by the Han. Yet that is not the worst of it. Beijing's programme assumes that relentless modernisation will result in the assimilation of the Uighurs. And just in case economic development does not eradicate their culture, China's coercive policies are supposed to finish the job. Uighurs are ordered to shave their beards and not fast at Ramadan. Prayer in public outside mosques is forbidden. Imams' sermons on Friday are restricted. The teaching of Arabic is allowed only in special schools sanctioned by the government, and Uighur-language instruction has been eliminated. In Kashgar, now known as Kashi, the government in February began razing the historic buildings and mosques in the Old City, ostensibly to root out the remnants of Uighur culture. Xinjiang? The Uighurs do not recognise the term, and they want their own nation. They proclaimed the East Turkestan Republic in 1944, but the new state did not last long. Mao Zedong crushed the Uighurs in 1949, the year he proclaimed the People's Republic of China. Now, Beijing calls the Turkic Muslims "Chinese", but that is a fiction. The Han and the Uighurs come from different racial stock, speak different languages and practise different religions. In short, the Uighurs are a conquered people. But they have not accepted Chinese domination. Han Beijing has the power to maintain its rule, but the local population is more sullen than compliant. Relations between the Han and Uighurs have historically been uneasy, but in recent years they have deteriorated, especially since early 1997 when fighting flared in Yining, the capital of the short-lived East Turkestan Republic. The unrest is thought to have led to at least several hundred deaths, and subsequent executions added to the toll. Since then, there have been scattered violent acts, such as those that occurred last year at the time of the Olympics. There is, despite what Beijing claims, no Uighur movement to speak of, but a formless opposition has been difficult to contain, especially because Han rule has been so unpopular. "There is not a day something is not happening in Xinjiang," said Erkin Alptekin, an exiled Uighur leader. Beijing has claimed the current protests were instigated from abroad, specifically by exiled Rebiya Kadeer and the World Uighur Congress. Given the apparent lack of co-ordination in the Uighur community, that is unlikely - and irrelevant in any case. The fundamental problem for the Chinese central government is simply that most Uighurs do not want to be part of the People's Republic. Therefore, nobody should have been surprised by events this week. Are the Uighurs employing violence? Yes. But that is the result of Beijing's policies, which triggered similar acts by the normally pacifist monks in Tibet in March 2008. Beijing's minority policies are abhorrent and unsustainable. As one observer said: "There's a fire burning in Xinjiang, and the Chinese can't extinguish it." Gordon G Chang is author of The Coming Collapse of China.