Why did the Tang Dynasty yearn for the Western Regions?

1. The western regions are close to the ruling center of the Tang Dynasty.

Chang 'an, the capital of the Tang Dynasty, is located in the northwest. And Li Tang ministers are mostly "Guanlong nobles", that is, Gansu in the northwest, not far from the western regions along the Hexi Corridor. So geographically and psychologically, the western regions are very close to the Tang Dynasty.

2. The war demand for Tubo and Tuyuhun.

Tubo and Tuguhun were enemies in the Tang Dynasty, and wars often occurred. Moreover, Tang Jun failed many times, even Chang 'an was breached by Tubo, who looted Chang 'an and established a puppet emperor. Tang Jun's conquest of the Western Regions will form a favorable strategic situation surrounding Tubo and Tuyuhun.