China was reunified in A.D. 589 by the short-lived Sui dynasty (A.D. 581-617), which has often been compared to the earlier Qin dynasty in tenure and the ruthlessness of its accomplishments. The Sui dynasty's early demise was attributed to the government's tyrannical demands on the people, who bore the crushing burden of taxes and compulsory labor. These resources were overstrained in the completion of the Grand Canal --a monumental engineering feat and in the undertaking of other construction projects, including the reconstruction of the Great Wall. Weakened by costly and disastrous military campaigns against Korea in the early seventh century, the dynasty disintegrated through a combination of popular revolts, disloyalty, and assassination.
Sui Dynasty rulers were partly Nomads, as was Tang Dynasty. Despite the fact that the royal houses of Sui and succeeding Tang were not entirely Han Chinese, both of these dynasties are considered to be Chinese, as opposed to the Mongols and Manchus later on.
Picture of Grand Canal.. the only thing that is uniquely Sui is the construction of Grand Canal, connecting Yellow and Yangtze two major eastward waterways by starting from Beijing all the way down to Hangzhou (link here), thus make nation wide commerce possible for the next prosperous Tang Dynasty.