In the Han Dynasty, following the principle of "focusing on the heavy and controlling the light", the establishment of the Central Army was put in the first place in the national armed construction. This is to maintain authoritarian centralization. It means to be dominant and very powerful, and to control other forces.
In the Han Dynasty, the military was more important than light:
It means that the emperor mastered and concentrated the most elite troops in the country around the capital, weakening the military strength in other places, which means "strong cadres and weak branches".
Therefore, the establishment of the "Central Army" is placed at the top of the national armed construction. The Southern Army and the Northern Army in the Western Han Dynasty were the powerful "Central Army". Whoever mastered the Northern and Southern Army could control the political situation. For example, after Lv Hou's death, zhou bo and Chen Ping used their stratagems to seize the command of the northern and southern armies from the Lushi people, and soon put an end to the rebellion between Zhu and Lu.