The four centuries from the breakdown of Han authority after 184 ce to the conquest of southern China by the Sui dynasty in 589 are by far the longest period of disunity and division that China has experienced since it was first brought under unified imperial rule by the Qin dynasty in 221 bce. Like other ages of division in Chinese history, the Six Dynasties period was marked by frequent, if not incessant, warfare, as a plethora of rival political authorities sought aggrandizement at the expense of their neighbors, and the most powerful and ambitious among them aimed to re-create, under their own authority, the lost imperial unity of Han times. As in other such periods, from the Warring States of the fourth century bce to the warlord era of the early twentieth century, division and conflict were conducive to the emergence of new military techniques and new methods of organizing both the state and its armies for success in war.