Update 1:
Please compare Tang Taizong and Tang Xuanzong!!!!!!!
Tang Taizong’s contribution to the Tang Dynasty was greater After Emperor Taizong of the Tang Dynasty came to the throne, because he witnessed the fall of the Sui Dynasty with his own eyes, he often used Emperor Sui Yang as a negative teaching material to warn himself and his subordinates. Like Xunzi, he compared the relationship between the people and the monarch to water and a boat. He realized that "water can carry a boat, but it can also capsize it." Therefore, he paid attention to the administration of officials, selected talents and appointed them, and followed advice. He only promotes talents, regardless of his background or grudges. Among the civil servants and generals, Wei Zheng was a Taoist priest and was an old minister of Prince Jiancheng. He once plotted to assassinate Taizong; Yu Chigong worked as a blacksmith and a subordinated general, but he was reused in both of them. Taizong encouraged his ministers to remonstrate directly. He gave more than 200 remonstrances before and after Wei Zheng, and directly stated his faults. Taizong accepted them all with an open mind and followed the good ones. After Wei Zheng's death, Taizong said sadly: "I use copper as a mirror to correct my clothes; I use the past as a mirror to know the ups and downs; I use people as a mirror to know gains and losses. When Wei Zheng passes away, I will be dead as a mirror." Picture reference ：china10k/mon/space Taizong paid special attention to agricultural production in the economy. He implemented the land equalization system and the rent-to-rent system, "eliminating luxuries, saving money, light corvees and low taxes", so that the people had enough food and clothing, and lived and worked in peace and contentment. In terms of culture, they vigorously rewarded academics and organized scribes to overhaul classics, justice and historical records; they set up the Imperial College in Chang'an and allowed the princes of the four barbarians to send their children to study abroad. In addition, Taizong repeatedly used troops abroad, and conducted military campaigns in all directions, including conquering the Eastern Turks, pacifying Xueyantuo, conquering Goryeo, conquering Tibet, and pacifying Uighurs, which spread the prestige of the Tang Dynasty far and wide. Taizong was revered as "Khan of Heaven" by the northwest countries and became the leader of the international alliance at that time. Image reference: china10k/mon/space In short, during the Zhenguan period (627-649 AD) when Emperor Taizong was in power, there was a peaceful and prosperous era of political clarity, economic development, social stability, and martial arts, which was known as the "Reign of Zhenguan" in history. Picture reference: china10k/mon/space After reading the Zhenguan period, everyone will definitely understand why to this day, the Chinese still call themselves "Tang people", and why there are "Chinatowns" all over the world. In the late Kaiyuan period, due to the long period of stability and prosperity, Tang Xuanzong gradually lost his previous spirit of striving to govern. After changing Yuan Tianbao, he indulged in pleasure, doted on Concubine Yang, trusted the eunuch Gao Lishi, and handed over all government affairs to Prime Minister Li Linfu. Li Linfu flattered Xuanzong in everything, but privately used his power to be arbitrary. After Lin Fu's death, Yang Guozhong, Yang Guifei's cousin, succeeded him as prime minister. He even excluded dissidents and engaged in corruption and bribery, which made politics increasingly corrupt. In addition, land annexation was fierce at that time, the gap between rich and poor was serious, and politics, economy, and society were gradually declining.
Reference: China Wannian.com
Tang Taizong Li Shimin's "Reign of Zhenguan" and Tang Xuanzong Li Longji's "Kaiyuan Prosperity" made ancient China's people-centered "benevolent government" Reaching its peak also brought the political, economic and cultural development level of China's feudal society to its peak. The production level of the prosperous Tang Dynasty was very high. According to records recorded in the fourth year of Tianbao by Emperor Xuanzong of the Tang Dynasty, the per capita grain yield per mu was more than 800 kilograms, which is equivalent to the highest level in the contemporary era. At that time, the land equalization system and renting system were implemented, and each male received 100 acres of land, of which 80 acres were divided into households, and he received 2 shi of millet per year. Calculated based on the harvest of 1 stone per mu, the harvest of 80 acres is 80 stones, and the land tax paid only accounts for 1/40 of his agricultural income. This is lighter than 1/30 of the "Government of Wenjing" and "Government of Mingzhang" in the Han Dynasty. In common terms, the Tang system: each person served the country for 20 days per year, which was lighter than the 30 days of the Han Dynasty. In terms of Tiao (Conquest of Cloth and Silk), each person paid 2 feet of damask and silk each year, which was only 1/6 of that of the Western Jin Dynasty. In the early Tang Dynasty, there were no exorbitant taxes on salt, wine, tea, etc. Because people's livelihood is prosperous, prices are very low. In the 4th year of Zhenguan, Emperor Taizong of the Tang Dynasty, the price of rice was 3 cents. In the 13th year of Kaiyuan, Emperor Xuanzong of Tang Dynasty, the price of rice in Luoyang was 10 cents, and in Qingzhou and Xuzhou, the price of rice was 5 cents. The country's grain depots, money depots, and cloth treasury are all full. For example, Qinghe in Hebei (a warehouse in the north of the Tang Dynasty). The small state city has more than 100,000 registered residents. During the Tianbao period, it stored more than 300,000 dendrobiums of grain, more than 3 million pieces of cloth, more than 800,000 pieces of silk, and more than 300,000 strings of money (a string worth a thousand dollars). So Du Fu wrote a poem: "Recalling the heyday of the Kaiyuan Dynasty, there were still thousands of houses in the small town, the rice was greasy and the corn was white, and the public and private warehouses were both abundant." At that time, the people not only lived and worked contentedly at home, but also traveled comfortably.
"Tongdian" records: During the Kaiyuan Dynasty, it reached Luoyang and Bianliang in the east and Qizhou in Guanzhong in the west. There were shops and restaurants along the road to entertain guests, and there were plenty of wine shops. Each post station rented donkeys and horses for guests to ride on. It reaches Jingxiang in the south, Taiyuan and Fanyang in the north, and Chunfu in Shuchuan in the west, all with inns and shops. Du Fu described that the posthouses from Qinzhou (now Tianshui, Gansu) to the Western Region (now Xinjiang) had ponds, marshes, forests, and bamboos. At that time, the posthouses from Gansu to Xinjiang had ponds and bamboos, which shows that the climate and water resources were much better than they are now. The culture of the prosperous Tang Dynasty also reached its peak in ancient China. Poet Li Bai, poetry sage Du Fu, painting sage Wu Daozi, grass sage Zhang Xu, as well as first-class calligraphers such as Yan Zhenqing, Liu Gongquan, Ouyang Xun, Chu Suiliang, and first-class musicians such as Li Guinian and Li Mu, Yu Wenkai First-rate architects, first-rate historians such as Liu Zhiji and Du You, first-rate Buddhists, translators and travelers such as Xuanzang, as well as the anonymous third generation who left their masterpieces in Dunhuang, Longmen and Datong. First-class sculptors and muralists all appeared in this glorious era. There is another data that can illustrate the stability and peace of society: very few people commit crimes among officials and people. In the fourth year of Zhenguan reign of Emperor Taizong of the Tang Dynasty, more than 20 people on death row were executed. In the 18th year of Emperor Xuanzong's founding of the Tang Dynasty, there were only 24 criminals in the country. From the "Government of Wenjing", "Government of Mingzhang", "Government of Zhenguan" to the "Kaiyuan Dynasty", there were no riots or uprisings by peasants or citizens (excluding power struggles among the court and nobles).