China's first imperial dynasty was the Qin dynasty (221–206 BC). The Qin unified the Chinese Warring States by conquest, but their empire became unstable after the death of the first emperor Qin Shi Huangdi. Within four years, the dynasty's authority had collapsed in the face of rebellion. Two former rebel leaders, Xiang Yu (d. 202 BC) of Chu and Liu Bang (d. 195 BC) of Han, engaged in a war to decide who would become hegemon of China, which had fissured into 18 kingdoms, each claiming allegiance to either Xiang Yu or Liu Bang. Although Xiang Yu proved to be a capable commander, Liu Bang defeated him at Battle of Gaixia (202 BC), in modern-day Anhui. Liu Bang assumed the title "emperor" (huangdi) at the urging of his followers and is known posthumously as Emperor Gaozu (r. 202–195 BC). Chang'an was chosen as the new capital of the reunified empire under Han.