The great Dynasty ruled China from 206BC to AD 220 and struck up an important silk trade with Europe. Citizens of the Roman Empire quickly developed a taste for silk togas. One branch of the transcontinental trade, know as the Southwest Silk Road, ran through to India. The Han emperor, wishing to control the entire trade route, launched the second Chinese invasion of Yunnan. The King of Dian welcomed the invaders, hoping his new allies would help him to subdue neighboring tribes; He thereupon received an imperial seal recognizing Dian as a tributary state. But the Chinese army could not get past Yunnan's formidable western mountains and eventually withdrew. Dian's tribal chiefs ruled in the name of the emperor and when the Han Dynasty finally collapsed, Yunnan continued on its own course as before. In time, the Dian kingdom weakened ands tribes from south seized power.