唐后期陇右失陷与京畿安全危机述略

The Loss of Longyou and Its Impact on the Security of the Imperial Capital in Late Tang Dynasty

在唐朝前期,黄河中下游的富庶农耕区和陇右东部可以养育马匹的半农半牧区,犹如国家强盛的左右臂膀。及至"安史之乱"后,吐蕃攻占陇右,唐之右臂断绝;河北与江淮间藩镇割据抗命,唐之左膀近乎瘫痪,帝国雄强气象,无由再振。从军事地理角度观察,陇右失陷对唐后期京畿安全的直接影响是关中暴露,京城危迫;党项部落东徙,扰攘关中十余年。间接影响是陇右的监牧丧失导致"马政"剧衰,若干羁縻府州及其部落兵损失,致使唐朝骑兵软弱,军力下降,综合国力严重削弱。而唐朝保卫京畿,缓解危机的重大措施,就是将关内道的军防重心从北面转到西面,即建立起京西、京北八镇军防新体系,阻遏戎寇,历经80余年顽强抗御,终使关中免沦左衽。

In the early period of Tang Dynasty, the fertile cultivated land in the middle and lower reaches of the Yellow River and the eastern region of Longyou, which is a half-agriculture and half-animal husbandry land and where horses are kept and raised, are two areas of crucial importance to the strength and integrity of the empire and serve like its two arms. After the Anshi Revolt, Longyou is seized by Tubo, a western ethnic group. Tangs right arm is thus broken. The region to the east of the capital, including the area from Hebei to the Youngtze River, is divided up by Fanzhen, local administrative and military divisions, in defiance of the central government. Tangs left arm is thus paralyzed. As a result, the mighty power of the empire is no more. From the perspective of military geography, the loss of Longyou means the immediate exposure of the Guanzhong Plain and the capital city to the outside threats. In the subsequent 10 years, for instance, the capital is harassed by the constant at- tacks from the Dangxiang tribe due to its eastern migration. The side effect of the loss of Longyou is the decline of horse-raising enterprise, shrinking of warriors from the Jimi administrative regions and local ethnic groups and the subsequent powerlessness of the mounted army. The power of the empire is drastically diminished. The important measure for the defense of the capital is to maneuver part of the military forces in Guanneidao from the north to the west to strengthen the western borderline. Eight military bases on the north and west sides of the capital is established to form a new defense system. In the subsequent 80-odd years, the new defense system proves to be effective in fighting against the aggressors from the western regions and ensures the security of the Guanzhong Plain.