First of all, Empress Wu, also known as Wu Zetian (624–705) was the only female emperor in China's history. She ruled the Tang Dynasty as empress (655–690), and then as Emperor for 15 years, in the seldom-mentioned Zhou Dynasty. During her long reign totaling 50 years, the empire became relatively stable, peaceful, powerful, and prosperous.
Secondly, There were four reasons leading to Tang's decline, among which the dominance of the eunuchs, the separatist regions of Fanzhen and clique conflicts were internal factors while peasants' uprising was the external factor. Moreover, as the dominance of eunuchs became serious, the military power of central regime was weakened.
Finally, printing, paper money, porcelain, tea, restaurants, gunpowder, the compass, and all of the things that Chinese of the Song Dynasty (A.D. 960-1280) gave to the world is AMAZING!