structural:reformatting, information:classification, structural:scholar_edition
Emperor Yang and re-conquest of Vietnam

Emperor Yang of Sui (569–618) ascended the throne after his father's death, possibly by murder. He further extended the empire, but unlike his father, did not seek to gain support from the nomads. Instead, he restored Confucian education and the Confucian examination system for bureaucrats. By supporting educational reforms, he lost the support of the nomads. He also started many expensive construction projects such as the Grand Canal of China, and became embroiled in several costly wars. Between these policies, invasions into China from Turkic nomads, and his growing life of decadent luxury at the expense of the peasantry, he lost public support and was eventually assassinated by his own ministers.

Both Emperors Yang and Wen sent military expeditions into Vietnam as Annam in northern Vietnam had been incorporated into the Chinese empire over 600 years earlier during the Han dynasty (202 BC – 220 AD). However the Kingdom of Champa in central Vietnam became a major counterpart to Chinese invasions to its north. According to Ebrey, Walthall, and Palais, these invasions became known as the Linyi-Champa Campaign (602–605).

The Hanoi area formerly held by the Han and Jin dynasties was easily retaken from the Early Lý dynasty ruler Lý Phật Tử in 602. A few years later the Sui army pushed farther south and was attacked by troops on war elephants from Champa in southern Vietnam. The Sui army feigned retreat and dug pits to trap the elephants, lured the Champan troops to attack then used crossbows against the elephants causing them to turn around and trample their own soldiers. Although Sui troops were victorious many succumbed to disease as northern soldiers did not have immunity to tropical diseases such as malaria.