Tang Taizong expanded China's borders north and west, reconquering lost land. Under his rule, China was returned to its rightful place. Tang Taizong improved agriculture and promoted foreign trade by expanding the network of roads and canals. He also restored China's vast bureaucracy of scholar-officials by expanding the civil service examination system. As the examination system became more and more important, talent and education overcame those who obtained power through noble birth.
Although the Tang rulers seemed to be completely helpful to restoring China, they induced stressful taxes while trying to cover the cost of military expansion. This plan, along with building programs, failed. The Tang dynasty finally was defeated at the Battle of Talas by the Muslim army. Central Asia passed out of Chinese control and into foreign hands. Chinese rebels sacked and burned the Tang capital at Ch'ang-an and murdered the last Tang emperor.
The empress during the campaign in Korea was Wu Zhao. She held the real power and assumed the title of emperor of China for herself, the only woman ever to do so.