The Uyghur are a Turkic ethnic group and are Muslims. They live mainly in the Xinjiang Autonomous Region (also called East Turkistan) in  northwestern China, where they were the largest ethnic group until the recent influx of Han Chinese (the  majority ethnic group within China). Uyghurs also live in several other Central Asian countries.

Origin of the conflict
Through history, the area of Turkestan has been ruled by different groups. It got the name Xinjiang after the Chinese conquest in 1759 by the Qing Dynasty. Advocates of Uyghur independence think this name is offensive (it means new territory or new frontier) and prefer to use Uyghurstan or Eastern Turkestan. In 1912, the Qing Dynasty was replaced by the Republic of China. In 1933 the self-proclaimed East Turkestan Republic was declared, but it was already brought under control of a Chines warlord a year later. It ruled the area the next decade with support from the Soviet Union. A Second East Turkestan Republic was founded in 1944 in northern Xinjiang and existed with Soviet support, but this Republic ended when the People's Liberation Army (PLA) entered Xinjiang in 1949. Independence and secessionist proponents in Xinjiang view the PLA entry as an invasion.

Chronological timeframe
With the recent influx of Han Chinese in the area, some Uyghurs believe that they are gradually being squeezed out, economically as well as politically. There have been several violent and ethnic clashes around Xinjiang. In 1997 various demonstrations and riots in Gulja is known as the Gulja Incident. The protests were fueled by  the execution of 30 Uyghur independence activists, and the severe measures taken against attempts to revive elements of traditional Uighur culture.
In 2008 a group of police officer have been attacked in Kashgar and sixteen of them died. The attackers Uyghurs, and it was suspected that the attack was a terrorist action by Eastern Turkistan separatists. However, the exiled president of the World Uyghur Congress (WUC), Rebiya Kadeer, condemned the reported attack and stated that "China is using the 2008 Olympics as an opportunity to further demonise the Uyghur people's legitimate and peaceful struggle and justify its heavy-handed repression in the region."
In the riots in Ürümqi (the capital city of the Xinjiang) that broke out on 5 July 2009, resulted in at least 150 persons to die. Officials say most of the dead were Han Chinese, but Uighur groups deny this. The initial confrontations between police and protesters soon turned into attacks on Hans. On 7 July, hundreds of armed Han people clashed with police and Uyghurs. Chinese President Hu Jintao leaves the G8 summit the day after and returned to China due to the situation in Xinjiang. The cause of the riots are controversial. The protests that preceded the riots were a response to the death of two Uighur workers in clashes with Han Chinese at a factory in southern China. However, the Chinese central government However, the Chinese central government blame the Xinjiang separatists based outside China for the unrest. Rebiya Kadeer has denied these charges.

Actors involved
The Chinese government says Uyghur militants have been waging a violent campaign for an independent state. They frequently refer to Uyghur nationalists as "terrorists", and received more global support for their own "war on terror" since 9/11.
Human rights organizations are concerned that this "war on terror" is being used as a pretext to repress ethnic Uyghurs. Activists say China has exaggerated the threat from Uyghur separatists to justify repression in the region.
With the recent influx of Han Chinese in the area, some Uyghurs believe that they are gradually being squeezed out, economically as well as politically.
There are also some Han People that are dissatisfied by government policies which they believe favour Uyghurs.

Response of the international community
The United Nations human rights chief was was "alarmed" over the high death toll in less than a day rioting. She also said China must treat detainees humanely in a way that adheres to international norms. The Secretary General Ban Ki-moon urged all sides to exercise restraint, and called on China to take measures to protect the civilian population and to respect the freedoms of citizens. The European Union expressed concern over the clashes, and urged the Chinese government to show restraint in dealing with the protests. There are also countries, like Afghanistan, Camodia, Russia and Sri Lanka, that regard the situation as an internal affair of China.

Sources
http://en.wikipedia.org/wiki/East_Turkestan
http://en.wikipedia.org/wiki/July_2009_%C3%9Cr%C3%BCmqi_riots
http://news.bbc.co.uk/2/hi/asia-pacific/8135203.stm
http://www.reuters.com/article/worldNews/idUSTRE5691HI20090710
http://www.hrw.org/press/2000/11/xinjiang1113-bck.htm
http://news.bbc.co.uk/2/hi/asia-pacific/7540636.stm