Answer:
1. Qin.
2. c. Local military rulers amassed more power.
Step-by-step explanation:
The defensive feature that the passage refers to is the Great Wall of China. The oldest existing section of wall was built by the Qi dynasty, and it was started around 685 BC. Other dynasties continued the construction, such as the Wei, Zhao, Han, Yan and Zhongshan.
One of the factors that contributed to the decline of the Han empire was the fact that several local military rulers began amassing too much power. The empire was fragmented, and divided into three spheres of influence: that of Cao Cao, that of Sun Quan and that of Liu Bei.