[Why] After the long accumulation through Zhenguan and the Wu Zhou period, Emperor Xuanzong of Tang on his ascension ruled with vigor and abolished long-standing bureaucratic ills. He vigorously developed production, and the empire's national strength was building toward the prosperous historical peak. [What] In the Kaiyuan era Xuanzong ruled with vigor, employing worthy chancellors like Yao Chong and Song Jing and overhauling redundant officialdom. Economically he promoted land reclamation, driving extreme commercial prosperity, with merchants from a myriad nations gathering at Chang'an at the absolute apex. [Who] Emperor Xuanzong Li Longji was the tragicomic emperor who in the first half of his life was wise and decisive and personally created the apex of medieval prosperity but in his late years foolish and brought disaster. Yao Chong was the enlightened chief chancellor of beneficial policy. [How] Kaiyuan prosperity is the recognized supreme dazzling apex of material wealth, cultural arts, and foreign exchange in classical Chinese society, called the High Tang aura. It became the imperishable prosperous memory of the Chinese nation.
Why
The historic event of Reign of Kaiyuan represents a key developmental peak of the Huaxia dynastic system. The absolute cosmopolitan peak of Tang prosperity and international prestige. By establishing this moral or administrative benchmark, it continues to shape the structural and philosophical fabric of ancient Chinese statecraft.