During the last years of the Sui Dynasty, peasant uprisings were raging everywhere in the country. Li Yuan, also known as Duke of Tang, a Sui general commanding the garrison at Taiyuan, staged a military revolt against the reign of Sui and in A.D. 618 finally proclaimed himself emperor, designating his reign as "Tang." He then conferred the title of Crown Prince on his eldest son Li Jiancheng. The second son Li Shimin became the Prince of Qin, and his youngest son Li Yuanjie, the Prince of Qi. Of the three brothers, the Prince of Qin was the most intelligent and made the greatest contribution towards the unification of the country since the mutiny in Taiyuan. Regarding Shimin as a substantial threat to his own position, the Crown Prince Jiancheng allied himself with the Prince of Qi in an attempt to get rid of Li Shimin by every means conceivable, thus sharply intensifying the contradictions between them. The Prince of Qin, on his part, realized that his dissolute father was a fatuous and incompetent person and that his brothers had repeatedly plotted against him. In these circumstances, he was driven beyond the limits of forbearance and so staged, in July, A.D. 626, a coup d'etat at Gate Xuan Wu  of the palace. He killed both the Crown Prince and the Prince of Qi, and Li Yuan was forced to abdicate the throne. Thus the Prince of Qin became Emperor Tai Zong of Tang, a sovereign hat was extolled in history as the "one emperor in millenium."

Emperor Tai Zong had himself lived through the tumultuous days of peasant uprising in the last years of the Sui Dynasty, and had witnessed the great strength of the laboring people in the rise and fall of the short-lived Sui Dynasty. All this had convinced him that the consolidation of his rule depended first and foremost on the pacification of the people. He often reminded himself of maxim of the great ancient philosopher Zhuangzi: the waters can both float and capsize a vessel. The people are like the waters, while the sovereign, a vessel. Bearing this in mind, Emperor Tai Zong introduced a series of political measures to improve the government and give the people a sense of security or even contentment. It was not long before the Tang Dynasty began to flourish, ushering in a famous period in Chinese history known as the "era of good government of Zhenguan."

The tow essential measures that accounted for Emperor Tai Zong's political success are: soliciting advice and picking the right man. With the former, he listened to different opinions and selected what was proper after careful study, and by the latter he granted appointments to officials according to their merits. Emperor Tai Zong once said to his ministers, "As a youngster, I like good bows and arrows. When once I had collected a dozen or so of fine bows, I thought smugly to myself that they were the best anyone could possess. But some bow makers told me after inspecting my collection that they were all rather inferior things. They said that though the wood was hard enough, the original timber was not exactly straight, and so the arrows would not sly straight. Only then did I realize that I was not discriminating enough as far as bow and arrow is concerned. And if I am not sufficiently knowledgeable about bows and arrows with which I have conquered all my opponents, how can I expect to know everything about the government of the empire?" Hence Emperor Tai Zong would always encourage his ministers to expostulate with him.

Wei Zheng, who was the most outspoken of all his ministers, would often argue vehemently with the Emperor, sometimes even making him wild with anger. However, Emperor Tai Zong usually felt afterwards that there was much sense in Wei's words, and so, placing special trust in him, he would consult with Wei on all-important matters.

Wei Zheng had served originally under the Crown Prince. He had tried his best to persuade the latter to do away with the Prince of Qin. After the coupd'etat at the palace gate of Xuan Wu, Tai Zong immediately sent for Wei Zheng and charged him with fomenting dissension among the brothers. Undaunted, Wei Zheng replied, "It's a pity that the Crown Prince had failed to heed my words. Otherwise, he situation would be entirely different." Tai Zong had long known of Wei Zheng's talent, and impressed now with his courage and insight, promoted him to the rank of councilor instead of punishing him. Later, he promoted Wei to rank equivalent to the Prime Minister, and made him one of his reliable aides.

Besides Wei Zheng, Emperor Tai Zong had also given official posts to some other talented people ho had in the past opposed him. This aroused the displeasure of those who had originally served under him. To them, Emperor Tai Zong explained with a smile, "The appointment of court officials is for administering the country. How can I have chumminess as a criterion in selecting officials?"

There was a Prime Minister of the Tang Dynasty named Ma Zhou, who had originally only been a retainer in a general's house with no official post at all. When Emperor Tai Zong read one of his articles on current administration written for the general, he appreciated it greatly and granted him an official position regardless of his credentials.

As Emperor Tai Zong was able to recognize merits and appoint people accordingly to proper posts , all his officials were dedicated heart and soul to the Tang Dynasty. In his life, Wei Zheng had remonstrated boldly with Tai Zong from time to time. On his death, Tai Zong was overwhelmed with grief an said to his ministers in tears, " With a bronze mirror, one can see if he is correctly attired; with history as one's mirror, he can understand the cause of the rise and fall of a nation; with men as mirror, one can see where he himself is right and wrong. Now that Wei Zheng is gone, I've lost my faithful mirror."