Kashgar, China, July 10, 2009--Uygur laborers harvest cotton on the outskirts of Kashgar, one of two cities in the Xinjiang Autonomous Region of western China, in a recent photograph.

This week's rioting in China, which state media said took at least 156 lives, has been tied to ethnic unrest between the Uygurs and China's Han majority. (See an interactive map of the peoples of China.)

Uygurs (also spelled "Uighurs") number about 8.4 million. The culture dates from the third and fourth centuries, when Turkic tribes were nomads roaming the region in search of pastures and oases.

Once a fabled stop on the Silk Road, Kashgar developed as the Uygurs gradually settled in the region to take up farming and trade. Outside the cities and their thriving markets, Uygur farmers irrigate their fields with an unique underground system of channels that brings water from the distant mountains.