The Han Dynasty saw the expansion of the Great Wall started by the Qin. The Capital was Chang’an in the upper highlands between the Yellow River (Huang He) and the Long River Yangtze).

 

Although the Qin Dynasty had previously united the diverse kingdoms of ancient China these links were still often tenuous. Regional leaders, often called warlords, were always a potential threat well into the reign of the Han Dynasties.

 

Annual Rainfall.  The Han dynasty is often considered a great hydrological empire. Waterwheels that powered wheat threshing machines were invented. Canal systems were built.