Transition from Sui to Tang

The transition from Sui to Tang refers to the transition period between the end of the Sui Dynasty and the start of the Tang Dynasty, when the former dynasty's territories were carved into a handful of short-lived states by its officials, generals, and agrarian rebel leaders, and the process of elimianation and annexation that followed which ultimately culminated in the consolidation of the Tang dynasty by the former Sui general Li Yuan. The transition started roughly around the year of 613 when Emperor Yang of Sui launched his first of three failed campaigns against Goguryeo, leading to a number of desertions in the army and the start of agrarian revolt against the Sui, and ended in 628, when Emperor Gaozu's son Li Shimin annexed the agrarian rebel ruler Liang Shidu's state of Liang, thereby once again unifying most of China under a single power.

As of 611, Sui Dynasty had just enjoyed more than two decades of peace and prosperity, as China had been united under it since it destroyed Chen Dynasty in 589, and aside from border conflicts with Eastern Tujue (which had since become a vassal state under its Qimin Khan Ashina Rangan) and Goguryeo, and one brief internal conflict between Emperor Yang of Sui, who became emperor in 604, and his brother Yang Liang the Prince of Han, the realm had not seen war. When Goguryeo's king Yeong-yang refused to pay homage to Emperor Yang in 610, Emperor Yang decided to plan a campaign to conquer it, and both he and the people believed that the conquest would be easy.

The logistics of staging the attack on Goguryeo, however, took much human and other tolls, as the building of a fleet and, particularly more so, the shipping of food and other supplies to the base of operations, Zhuo Commandery (涿郡, roughly modern Beijing), caused major disruptions in the farming cycle and major deaths in those conscripted to ship the supplies to Zhuo Commandery. In response, in 611, in northern China, those who were unwilling to be conscripted began to rise as agrarian rebels, led by leaders such as Wang Bo (王薄) and Liu Badao (劉霸道), and while Emperor Yang initially did not consider these rebels serious threats, the local governmental militias were unable to quell them.

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