Editing Sichuan (section)

===Qin dynasty===
The rulers of the expansionist state of [[Qin (state)|Qin]], based in present-day [[Gansu]] and [[Shaanxi]], were the first strategists to realize that the area's military importance matched its commercial and agricultural significance. The Sichuan basin is surrounded by the [[Hengduan Mountains]] to the west, the [[Qin Mountains]] to the north, and [[Yungui Plateau]] to the south. Since the Yangtze flows through the basin and then through the perilous Three Gorges to eastern and southern China, Sichuan was a staging area for amphibious military forces and a haven for political refugees.{{citation needed|date=June 2015}}

Qin armies finished their conquest of the kingdoms of Shu and Ba by 316 BC. Any written records and civil achievements of earlier kingdoms were destroyed. Qin administrators introduced improved agricultural technology. [[Li Bing (Qin)|Li Bing]], engineered the [[Dujiangyan irrigation system]] to control the [[Min River (Sichuan)|Min River]], a major [[tributary]] of the Yangtze. This innovative hydraulic system was composed of movable weirs which could be adjusted for high or low water flow according to the season, to either provide irrigation or prevent floods. The increased agricultural output and taxes made the area a source of provisions and men for Qin's unification of China.{{citation needed|date=April 2020}}