The territorial expansion of the Western Han, notably under Emperor Wudi, placed considerable stress on the maintenance of the army. In the first place, military force was deployed to take new territory, particularly in the northwest, where huge tracts were occupied beyond the Jade Gates into the Tarim Basin. To the south, the Han Empire was extended as far as the rich Hong (Red) River Basin in Vietnam, and colonization also extended into the Korean Peninsula. Thereafter, it was necessary to provide for frontier defense, particularly along the extended Great Wall, where the Xiongnu were a constant threat. There was also a problem of security within the empire itself, newly founded after the long Warring States period, for provincial discontent and uprisings, such as those of the Red Eyebrows and the YELLOW TURBANS, were always possible.
To provide for the army, military conscription was compulsory except for top aristocrats and, on occasion, those who could afford to buy exemption. At the age of 23, men underwent a year of military training in their home commandery, in the infantry, cavalry, or navy. Then they were posted for another year to active service, which could involve guard duties at the capital or frontier defense. Thereafter, they could return home but remained in a state of readiness for recall. Under the Western Han, they were required to return regularly for further training until they reached the age of 56. There was also the so-called Northern Army, a force of regulars under five commanders who served as guards of the capital and of the passes leading into the heartland of the empire, the Wei Valley. This force numbered about 3,500 men. If war threatened, as, for example, with Xiongnu incursions in the north, the militia reserve could be called up and deployed. Militia units were also assembled in the event of internal threats to security. With the Yellow Turban uprising of 184 C. E., there was a major mobilization appointment of a military commander with the title general of chariots and cavalry.
The growing administrative machine and maintenance of a standing army, not to mention the need to conscript young men into military training, placed major demands on agricultural production. An efficient rural sector and the ability to gather taxes were essential for the survival of the state.
The Yellow Turbans participated in a major insurrection against the Eastern Han emperor LINGDI and his administration. Lingdi (156-89 C. E.) was one of the few later emperors of the Eastern HAN DYNASTY who lived long enough to have a political impact. Early in his reign when he was still a boy, there was a power struggle between the old court families and the eunuchs. The latter prevailed, and until the end of the reign they dominated the central administration, favoring their relatives and opening administrative positions for sale. At the same time, new methods of taxation were devised, and the system of providing central aid to commanderies suffering crop failures began to break down. This led to serious disaffection in the countryside. There were many local insurrections, the most serious instigated by Zhang Que. He was the leader of a sect that claimed that every 60 years a new cycle of peace and prosperity began and that the next cycle, due to begin in 184 C. E., entailed the end of the Han dynasty. Through the organization of the Yellow Turbans, which would now be described as terrorist cells, Zhang Que fomented a simultaneous uprising across 16 commanderies that stretched the defenses of the court to the limit. Military defeat in one area did not bring the rebellion as a whole to an end, for although Zhang Que himself died in the year of the rebellion, the Yellow Turban movement continued to create disturbances in the provinces for many years. Some Chinese historians, influenced by the importance of peasant revolts, have identified the Yellow Turbans as the cause of the fall of the Eastern Han dynasty, but this claim is probably exaggerated.