Who initiated Yuanjia's rule in Liu and Song Dynasties?

After the Song Dynasty in Liu Yujian, a series of reforms were carried out in order to revitalize the new dynasty. After his death, his eldest son Liu Yifu succeeded to the throne. Liu Yifu indulged in pleasure all day long, but ignored state affairs, and was soon deposed. The third son, Liu Yilong, ascended the throne. This is Song Wendi. He is a very successful emperor. He inherited the cause of the previous generation and carried out reforms: politically, he rectified the bureaucracy, strengthened the inspection and supervision of local officials, relaxed the punishment and appealed for talents; Economically, he built water conservancy projects, rewarded agricultural weaving, reduced taxes and actively carried out disaster relief activities; In the social ideological and cultural construction, he vigorously developed education. In this way, a good situation of political clarity and social stability appeared in Liu and Song Dynasties. Song Wendi's country name is Yuanjia, so this period of Qingming is called "the rule of Yuanjia" in history.