Uighur women grieve for their men who they claim were taken away by Chinese authorities after Sunday's protest in Urumqi, China, Tuesday, July 7 , 2009. Urumqi was tense Tuesday, with protests happening in several parts of the city and both Han Chinese and Uighur groups facing off with armed police.

The Chinese government blanketed Urumqi, the capital of China's far western Xinjiang region, with 20,000 new security troops on Wednesday, as thousands of residents began to flee following the deadly ethnic clashes that erupted over the weekend. 

The unrest has become a major challenge for this country's Communist leaders. In a sign of their growing concern about the situation, President Hu Jintao canceled plans to attend the Group of Eight summit in Italy and rushed home early Wednesday. 

Sean Roberts, director of the International Development Studies Program at George Washington University, who has been studying the Uighurs for about 20 years and who has authored numerous articles about the Uighur communities of Kazakhstan and China, was online Wednesday, July 8, at 1 p.m. ET to talk about the conflict. 

In an e-mail interview with washingtonpost.com, Roberts said, "The current unrest in Xinjiang is another chapter in a long history of tensions between Han Chinese and Uyghurs, but it is mostly the result of the frustrations experienced by Uyghurs over the last decade as the rapid pace of Chinese development in the region has brought scores of Han Chinese migrants to Xinjiang and has displaced Uyghurs from their traditional livelihoods and communities. While the violence that has emerged on both sides of the conflict is shocking, the most surprising aspect of the events may be that the tensions had not boiled over into direct confrontations until now."