In 589 CE, after almost four centuries, China was reunited for the first time since the end of the Han era. The intervening four hundred years, often referred to as the Six Dynasties Period, was marked by political struggle and military strife on a level not seen in China in over a millennium. Yet while many histories describe the Six Dynasties era as a China's version of Europe's "dark ages," it was also a period of great cultural intermingling. Various Central and Western Asian peoples settled in the north regions of China, and local populations migrated en masse from area to area in search of new lands to settle. The various cultural elements introduced during these four centuries were further unified and Sinicized when the Sui achieved a new unification of China. This synthesis would reach its culmination in the distinctive culture of the Tang dynasty, which came to power after the downfall of the second Sui emperor.

Though the Sui dynasty ruled only for approximately thirty years, much was accomplished by the first emperor Wendi (reigned 581-604), formerly a general for the Northern Zhou dynasty. Among Wendi's many accomplishments was a restructuring of the government to simplify internal administration, a revision of the penal code, and a number of public work projects, including the creation of a complex canal system joining the Yellow, Huai and Yangzi Rivers. Wendi was also a supporter of Buddhism, and encouraged the spread of the religion throughout his domain.

Wendi also took steps to protect the frontiers of his new empire. To the north was the domain of the Yuezhi, a confederacy of nomadic warriors of Turkic heritage. The Yuezhi controlled the Mongolian steppes from Manchuria to the edge of the Byzantine Empire in the west; internally, however, the confederacy was undergoing a split into two rival groups, one controlling the western half of Yuezhi territory and one controlling the eastern. Wendi offered his support to the Western Yuezhi, and worked to undermine the strength and authority of the Eastern Yuezhi khan. These political machinations, as well as a reinforced Great Wall and an increase in the number of troops patrolling the northern borders greatly reduced the threat of attack by the Eastern Yuezhi. Simultaneous, this policy also allowed for the reopening of the western trade routes, and once again a prosperous trade relationship with Central and Western Asia was developed.

Wendi's successor was Yangdi (568-618), who in many ways was even more ambitious than his father. Yangdi built a second capital at Loyang in the east to complement that constructed by Wendi at Changan. He oversaw the return of the southernmost regions of China into the empire, and the addition of the Champa kingdom in Vietnam. Yet it was Yangdi's ambition (combined with financial mismanagement) that ultimately led to the loss of the empire. His attempts to meddle in the internal politics of his nomadic neighbors led to the alienation of the western Yuezhi faction, which wrested away control of the city-states of the Tarim Basin, formerly under Sui protection.

In 612 Yangdi began a series of campaigns to subdue the Korean kingdom of Koguryo, which had until then refused to offer tribute. Disastrous flooding compounded the cost of these failed campaigns, both in terms of resources and human life. Within a few years rebellion broke out throughout the empire, and in 618 Yangdi was killed by his own attendants. The general Li Yuan staged an attack on the would-be usurpers, and captured the Sui capital of Changan. There he proclaimed himself the first emperor of a new dynasty, the Tang, which would rule China for the next three hundred years.